Investment Securities and Fair Value Measurements
 3 Months Ended
Mar. 31, 2018
Fair Value Disclosures [Abstract]  
Investment Securities and Fair Value Measurements
Investment Securities and Fair Value Measurements
Investment Securities
Investment securities classified as available-for-sale consisted of the following at March 31, 2018 and December 31, 2017 (in thousands):
 
March 31, 2018
 
Amortized Cost
 
Gross Unrealized Gains
 
Gross Unrealized Losses
 
Estimated Fair Value
Corporate bonds
$
37,976

 
$
—

 
$
(299
)
 
$
37,677

Agency securities
11,034

 
1

 
(52
)
 
10,983

Certificates of deposit
1,986

 
—

 
(2
)
 
1,984

Treasury securities
8,622

 
—

 
(5
)
 
8,617

Total available-for-sale investment securities
$
59,618

 
$
1

 
$
(358
)
 
$
59,261

 
December 31, 2017
 
Amortized Cost
 
Gross Unrealized Gains
 
Gross Unrealized Losses
 
Estimated Fair Value
Corporate bonds
$
38,383

 
$
—

 
$
(166
)
 
$
38,217

Agency securities
11,045

 
—

 
(42
)
 
11,003

Certificates of deposit
2,982

 
1

 
(2
)
 
2,981

Total available-for-sale investment securities
$
52,410

 
$
1

 
$
(210
)
 
$
52,201


As of March 31, 2018, the unrealized losses on investment securities which have been in a net loss position for twelve months or greater were not material. These unrealized losses are considered temporary and there were no impairments considered to be "other-than-temporary" based on our evaluation of available evidence, which includes our intent to hold these investments to maturity or a recovery of the cost basis.
At March 31, 2018 and December 31, 2017, the contractual maturities of our investments did not exceed 36 months. The fair values of available-for-sale investments, by remaining contractual maturity, are as follows (in thousands):
 
March 31, 2018
 
December 31, 2017
 
Amortized Cost
 
Estimated Fair Value
 
Amortized Cost
 
Estimated Fair Value
Due in 1 year or less
$
37,410

 
$
37,290

 
$
29,850

 
$
29,800

Due after 1 year through 3 years
22,208

 
21,971

 
22,560

 
22,401

Total available-for-sale investment securities
$
59,618

 
$
59,261

 
$
52,410

 
$
52,201

During the three months ended March 31, 2018 and 2017, we had sales and maturities (which includes calls) of investment securities, as follows (in thousands):
 
Three Months Ended March 31, 2018
 
Gross Realized Gains
 
Gross Realized Losses
 
Gross Proceeds from Sales
 
Gross Proceeds from Maturities
Corporate bonds
$
—

 
$
—

 
$
—

 
$
6,300

Agency securities
—

 
—

 
—

 
1,000

Certificates of deposit
—

 
—

 
—

 
996

Treasury securities
—

 
—

 
5

 
—

 
$
—

 
$
—

 
$
5

 
$
8,296

 
Three Months Ended March 31, 2017
 
Gross Realized Gains
 
Gross Realized Losses
 
Gross Proceeds from Sales
 
Gross Proceeds from Maturities
Corporate bonds
$
—

 
$
—

 
$
—

 
$
3,200

Certificates of deposit
—

 
—

 
—

 
1,245

 
$
—

 
$
—

 
$
—

 
$
4,445


For the three months ended March 31, 2018 and 2017, we received interest income net of the amortization and accretion of the premium and discount of $0.2 million and $0.1 million, respectively.
Fair Value Measurements
Recurring Fair Value Measurements
Financial assets and financial liabilities are classified in their entirety based on the lowest level of input that is significant to the fair value measurement. The following tables summarize our financial assets measured at fair value on a recurring basis as of March 31, 2018 and December 31, 2017, by level within the fair value hierarchy (in thousands):
 
March 31, 2018
 
Level 1
 
Level 2
 
Level 3
 
Total Fair
Value
Cash equivalents:
 
 
 
 
 
 
 
Money market funds
$
107

 
$
—

 
$
—

 
$
107

Available-for-sale investment securities:
 
 
 
 
 
 
 
Corporate bonds
—

 
37,677

 
—

 
37,677

Agency securities
—

 
10,983

 
—

 
10,983

Certificates of deposit
1,984

 
—

 
—

 
1,984

  Treasury securities
8,617

 
—

 
—

 
8,617

Total
$
10,708

 
$
48,660

 
$
—

 
$
59,368

 
December 31, 2017
 
Level 1
 
Level 2
 
Level 3
 
Total Fair
Value
Cash equivalents:
 
 
 
 
 
 
 
Money market funds
$
5,524

 
$
—

 
$
—

 
$
5,524

Available-for-sale investment securities:
 
 
 
 
 
 
 
Corporate bonds
—

 
38,217

 
—

 
38,217

Agency securities
—

 
11,003

 
—

 
11,003

Certificates of deposit
2,981

 
—

 
—

 
2,981

Total
$
8,505

 
$
49,220

 
$
—

 
$
57,725

The carrying amounts of cash equivalents, restricted cash, accounts receivable, accounts payable and accrued liabilities approximate fair value because of the short maturity of these items.
There were no changes to our valuation techniques used to measure asset and liability fair values on a recurring basis during the three months ended March 31, 2018. The valuation techniques for the items in the table above are as follows:
Cash Equivalents
As of March 31, 2018 and December 31, 2017, cash equivalents include cash invested in money market funds. Fair value is based on market prices for identical assets.
Available-for-Sale Investment Securities
The fair value of our corporate bonds and agency securities is based on pricing determined using inputs other than quoted prices that are observable either directly or indirectly such as yield curve, volatility factors, credit spreads, default rates, loss severity, current market and contractual prices for the underlying instruments or debt, broker and dealer quotes, as well as other relevant economic measures. The fair value of our certificates of deposit and treasury securities is based on market prices for identical assets.
Non-Recurring Fair Value Measurements
Certain assets, including goodwill, intangible assets and our note receivable with SecureDocs, are also subject to measurement at fair value on a non-recurring basis using Level 3 measurement, but only when they are deemed to be impaired as a result of an impairment review. For the three months ended March 31, 2018 and 2017, no impairments were identified on those assets required to be measured at fair value on a non-recurring basis.