Investments
 12 Months Ended
Dec. 31, 2019
Investments, Debt and Equity Securities [Abstract]  
Investments Investments
We have designated our investment portfolio as available-for-sale and report it at fair value. The related unrealized gains and losses are, after considering the related tax expense or benefit, recognized through comprehensive income and loss, and on an accumulated basis in shareholders' equity. Net realized investment gains and losses are reported in earnings based on specific identification of securities sold or other-than-temporarily impaired.
Fair Values and Gross Unrealized Gains and Losses on Investments
 
Amortized
Cost
 
Gross Unrealized
 
Fair
Value
 
 
Gains
 
Losses
 
As of December 31, 2019
(In Thousands)
U.S. Treasury securities and obligations of U.S. government agencies
$
48,203

 
$
784

 
$
(58
)
 
$
48,929

Municipal debt securities
189,530

 
1,721

 
(1,035
)
 
190,216

Corporate debt securities
661,719

 
23,373

 
(211
)
 
684,881

Asset-backed securities
170,153

 
2,603

 
(114
)
 
172,642

Total bonds
1,069,605

 
28,481

 
(1,418
)
 
1,096,668

Short-term investments
44,174

 
98

 
—

 
44,272

Total investments
$
1,113,779

 
$
28,579

 
$
(1,418
)
 
$
1,140,940

 
Amortized
Cost
 
Gross Unrealized
 
Fair
Value
 
 
Gains
 
Losses
 
As of December 31, 2018
(In Thousands)
U.S. Treasury securities and obligations of U.S. government agencies
$
48,171

 
$
35

 
$
(1,376
)
 
$
46,830

Municipal debt securities
92,014

 
206

 
(963
)
 
91,257

Corporate debt securities
554,079

 
847

 
(11,688
)
 
543,238

Asset-backed securities
171,990

 
792

 
(1,457
)
 
171,325

Total bonds
866,254

 
1,880

 
(15,484
)
 
852,650

Short-term investments
58,733

 
107

 
—

 
58,840

Total investments
$
924,987

 
$
1,987

 
$
(15,484
)
 
$
911,490


    We did not own any mortgage-backed securities in our asset-backed securities portfolio at December 31, 2019 or 2018.
The following table presents a breakdown of the fair value of our corporate debt securities by issuer industry group as of December 31, 2019 and 2018:
 
December 31, 2019
 
December 31, 2018
Financial
38
%
 
38
%
Consumer
26

 
27

Communications
10

 
12

Utilities
9

 
7

Industrial

8

 
7

Technology
7

 
6

Energy
2

 
2

Other
—

 
1

Total
100
%
 
100
%

As of December 31, 2019 and 2018, approximately $5.5 million and $5.3 million, respectively, of our cash and investments were held in the form of U.S. Treasury securities on deposit with various state insurance departments to satisfy regulatory requirements.
Scheduled Maturities
The amortized cost and fair values of available-for-sale securities as of December 31, 2019 and 2018, by contractual maturity, are shown below. Expected maturities will differ from contractual maturities because issuers may have the right to call or prepay obligations with or without call or prepayment penalties. Because most asset-backed securities provide for periodic payments throughout their lives, they are listed below in a separate category.
As of December 31, 2019
Amortized
Cost
 
Fair
Value
 
(In Thousands)
Due in one year or less
$
138,776

 
$
139,113

Due after one through five years
406,986

 
417,208

Due after five through ten years
380,737

 
394,180

Due after ten years
17,127

 
17,797

Asset-backed securities
170,153

 
172,642

Total investments
$
1,113,779

 
$
1,140,940


As of December 31, 2018
Amortized
Cost
 
Fair
Value
 
(In Thousands)
Due in one year or less
$
76,087

 
$
76,104

Due after one through five years
352,282

 
347,701

Due after five through ten years
318,728

 
310,633

Due after ten years
5,900

 
5,727

Asset-backed securities
171,990

 
171,325

Total investments
$
924,987

 
$
911,490


Aging of Unrealized Losses
As of December 31, 2019, the investment portfolio had gross unrealized losses of $1.4 million, of which $0.1 million had been in an unrealized loss position for a period of 12 months or greater. We did not consider these securities to be other-than-temporarily impaired as of December 31, 2019. We based our conclusion that these investments were not other-than-temporarily impaired as of December 31, 2019 on the following facts: (i) the unrealized losses were primarily caused by interest rate movements and market fluctuations in credit spreads since the purchase date, (ii) we do not intend to sell these investments; and (iii) we do not believe that it is more likely than not that we will be required to sell these investments before recovery of our amortized cost basis, which may not occur until maturity. For those securities in an unrealized loss position, the length of time the securities were in such a position is as follows:
 
Less Than 12 Months
 
12 Months or Greater
 
Total
 
# of Securities
Fair Value
Unrealized Losses
 
# of Securities
Fair Value
Unrealized Losses
 
# of Securities
Fair Value
Unrealized Losses
As of December 31, 2019
 
(Dollars in Thousands)
U.S. Treasury securities and obligations of U.S. government agencies
4

$
12,001

$
(58
)
 
—

$
—

$
—

 
4

$
12,001

$
(58
)
Municipal debt securities
26

92,844

(1,034
)
 
1

999

(1
)
 
27

93,843

(1,035
)
Corporate debt securities
10

30,481

(140
)
 
14

23,976

(71
)
 
24

54,457

(211
)
Asset-backed securities
9

19,236

(102
)
 
1

2,988

(12
)
 
10

22,224

(114
)
Total
49

$
154,562

$
(1,334
)
 
16

$
27,963

$
(84
)
 
65

$
182,525

$
(1,418
)
 
Less Than 12 Months
 
12 Months or Greater
 
Total
 
# of Securities
Fair Value
Unrealized Losses
 
# of Securities
Fair Value
Unrealized Losses
 
# of Securities
Fair Value
Unrealized Losses
As of December 31, 2018
 
(Dollars in Thousands)
U.S. Treasury securities and obligations of U.S. government agencies
—

$
—

$
—

 
19

$
41,817

$
(1,376
)
 
19

$
41,817

$
(1,376
)
Municipal debt securities
4

7,409

(11
)
 
31

58,658

(952
)
 
35

66,067

(963
)
Corporate debt securities
118

226,477

(3,952
)
 
126

221,675

(7,736
)
 
244

448,152

(11,688
)
Asset-backed securities
25

36,017

(1,136
)
 
22

33,988

(321
)
 
47

70,005

(1,457
)
Total
147

$
269,903

$
(5,099
)
 
198

$
356,138

$
(10,385
)
 
345

$
626,041

$
(15,484
)
Net Investment Income
The following table presents the components of net investment income:
 
For the year ended December 31,
 
2019
 
2018
 
2017
 
(In Thousands)
Investment income
$
31,332

 
$
24,342

 
$
17,046

Investment expenses
(476
)
 
(804
)
 
(773
)
Net investment income
$
30,856

 
$
23,538

 
$
16,273


The following table presents the components of net realized investment gains:
 
For the year ended December 31,
 
2019
 
2018
 
2017
 
(In Thousands)
Gross realized investment gains
$
561

 
$
525

 
$
546

Gross realized investment losses
(516
)
 
(468
)
 
(338
)
Net realized investment gains
$
45

 
$
57

 
$
208


Investment Securities - Other-than-Temporary Impairment (OTTI)
As of December 31, 2019, 2018 and 2017, we held no other-than-temporarily impaired securities. For the years ended December 31, 2019 and 2017, we recognized $0.4 million and $0.1 million of OTTI losses in earnings, respectively. For the year ended December 31, 2018 we did not recognize any OTTI losses. There were no credit losses recognized in earnings for which a portion of an OTTI loss was recognized in AOCI (loss) for any period presented.