Investment securities
 12 Months Ended
Dec. 31, 2014
Investments, Debt and Equity Securities [Abstract]  
Investment securities

Investment securities
 
Investment securities at December 31, 2014 and 2013 consisted of the following (dollars in thousands):
 
Amortized
cost
 
Gross
unrealized
gains
 
Gross
unrealized
losses
 
Estimated
fair value
2014
 

 
 

 
 

 
 

Available-for-sale
 

 
 

 
 

 
 

U.S. Agency mortgage-backed securities (MBS) *
$
232,514

 
$
4,562

 
$
(896
)
 
$
236,180

Non-agency MBS
66,872

 
232

 
(407
)
 
66,697

U.S. Agency asset-backed securities
8,192

 
858

 
(42
)
 
9,008

Corporate debt securities
7,333

 
137

 
—

 
7,470

Mutual fund
514

 
13

 
—

 
527

 
$
315,425

 
$
5,802

 
$
(1,345
)
 
$
319,882

Held-to-maturity
 

 
 

 
 

 
 

U.S. Agency mortgage-backed securities (MBS)
$
110,175

 
$
2,032

 
$
—

 
$
112,207

Tax credit investments
564

 
—

 
—

 
564

Obligations of state and political subdivisions
41,840

 
962

 
(18
)
 
42,784

 
$
152,579

 
$
2,994

 
$
(18
)
 
$
155,555

 
 
 
 
 
 
 
 
2013
 

 
 

 
 

 
 

Available-for-sale
 

 
 

 
 

 
 

U.S. Agency MBS *
$
171,853

 
$
3,125

 
$
(3,646
)
 
$
171,332

Non-agency MBS
13,500

 
11

 
(414
)
 
13,097

U.S. Agency asset-backed securities
8,683

 
887

 
(21
)
 
9,549

Mutual fund
502

 
1

 
—

 
503

 
$
194,538

 
$
4,024

 
$
(4,081
)
 
$
194,481

Held-to-maturity
 

 
 

 
 

 
 

Tax credit investments
$
614

 
$
—

 
$
—

 
$
614

Obligations of state and political subdivisions
706

 
22

 
—

 
728

 
$
1,320

 
$
22

 
$
—

 
$
1,342

 
* U.S. Agency MBS included private label MBS of approximately $9.3 million and $11.3 million at December 31, 2014 and 2013, respectively, which are supported by FHA/VA collateral.
  
The following table presents the fair value and gross unrealized losses of the Bank’s investment securities, aggregated by investment category and length of time that individual securities have been in a continuous unrealized loss position, at December 31, 2014 and 2013 (dollars in thousands):
 
Less than 12 months
 
12 months or more
 
Total
 
Estimated 
fair value
 
Unrealized
losses
 
Estimated 
fair value
 
Unrealized
losses
 
Estimated 
fair value
 
Unrealized
losses
2014
 

 
 

 
 

 
 

 
 

 
 

Available-for-sale
 
 
 
 
 
 
 
 
 
 
 
U.S. Agency MBS
$
15,807

 
$
(17
)
 
$
41,479

 
$
(879
)
 
$
57,286

 
$
(896
)
Non-Agency MBS
23,953

 
(220
)
 
6,411

 
(187
)
 
30,364

 
(407
)
U.S. Agency asset-backed securities
718

 
(6
)
 
1,582

 
(36
)
 
2,300

 
(42
)
 
$
40,478

 
$
(243
)
 
$
49,472

 
$
(1,102
)
 
$
89,950

 
$
(1,345
)
 
 
 
 
 
 
 
 
 
 
 
 
Held-to-maturity
 
 
 
 
 
 
 
 
 
 
 
U.S. Agency MBS
$
—

 
$
—

 
$
—

 
$
—

 
$
—

 
$
—

Obligations of state and political subdivisions
3,806

 
(18
)
 
—

 
—

 
3,806

 
(18
)
 
$
3,806

 
$
(18
)
 
$
—

 
$
—

 
$
3,806

 
$
(18
)
 
 
 
 
 
 
 
 
 
 
 
 
2013
 

 
 

 
 

 
 

 
 

 
 

Available-for-sale
 
 
 
 
 
 
 
 
 
 
 
U.S. Agency MBS
$
35,440

 
$
(810
)
 
$
30,779

 
$
(2,836
)
 
$
66,219

 
$
(3,646
)
Non-Agency MBS
9,569

 
(412
)
 
179

 
(2
)
 
9,748

 
(414
)
U.S. Agency asset-backed securities
703

 
(4
)
 
1,775

 
(17
)
 
2,478

 
(21
)
 
$
45,712

 
$
(1,226
)
 
$
32,733

 
$
(2,855
)
 
$
78,445

 
$
(4,081
)


The unrealized losses on investments in U.S. Agency and non-agency MBS and U.S. Agency asset-backed securities are primarily due to elevated yield/rate spreads at December 31, 2014 and 2013 as compared to yield/rate relationships prevailing at the time specific investment securities were purchased. Management expects the fair value of these investment securities to recover as market volatility lessens and/or as securities approach their maturity dates. Accordingly, management does not believe that the above gross unrealized losses on investment securities are other-than-temporary. No impairment adjustments have been recorded for the years ended December 31, 2014, 2013 and 2012.

Management intends to hold the investment securities classified as held-to-maturity until they mature, at which time the Company will receive full amortized cost value for such investment securities. Furthermore, as of December 31, 2014, management did not have the intent to sell any of the securities classified as available-for-sale in the table above and believes that it is more likely than not that the Company will not have to sell any such securities before a recovery of cost.

The amortized cost and estimated fair value of investment securities at December 31, 2014, by contractual maturity, are shown below (dollars in thousands). Expected maturities will differ from contractual maturities because borrowers may have the right to call or prepay obligations with or without call or prepayment penalties.
 
Available-for-sale
 
Held-to-maturity
 
Amortized
cost
 
Estimated
fair value
 
Amortized
cost
 
Estimated
fair value
Due in one year or less
$
377

 
$
379

 
$
195

 
$
201

Due after one year through five years
13,883

 
13,914

 
19,331

 
19,377

Due after five years through ten years
71,304

 
70,826

 
102,002

 
104,190

Due after ten years
229,347

 
234,236

 
30,487

 
31,223

Mutual fund
514

 
527

 
—

 
—

Tax credit investments
—

 
—

 
564

 
564

 
$
315,425

 
$
319,882

 
$
152,579

 
$
155,555


 
Investment securities with an estimated fair value of approximately $187.3 million and $171.1 million at December 31, 2014 and 2013, respectively, were pledged or in the process of being pledged, to secure various borrowings and for other purposes as required or permitted by law.
 
The Company sold $63.5 million and $0.4 million of investment securities during the years ended December 31, 2014 and 2013, respectively. The Company sold no securities during the year ended December 31, 2012.