6. Fair Value Measurements

Our assets and liabilities subject to fair value measurements on a recurring basis and the required disclosures:

	Fair		Fair Value Measurements
	Value		Using Fair Value Hierarchy
As of March 31, 2015	Total		Level 1		Level 2		Level 3
Assets:
Cash and cash equivalents	$	27,759	$	27,759	$	—	$	—
Corporate bonds		21,546		21,546		—		—
Mortgage-backed and asset-backed securities		966		966		—		—
Agency bonds		300		300		—		—
Marketable securities		22,812		22,812		—		—
Deferred compensation plan investments		973		973		—		—
Assets at fair value	$	51,544	$	51,544	$	—	$	—
Liabilities:
Interest rate swap	$	437	$	—	$	437	$	—
Deferred compensation		913		913		—		—
Liabilities at fair value	$	1,350	$	913	$	437	$	—

	Fair		Fair Value Measurements
	Value		Using Fair Value Hierarchy
As of December 31, 2014	Total		Level 1		Level 2		Level 3
Assets:
Cash and cash equivalents	$	26,922	$	26,922	$	—	$	—
Corporate bonds		21,704		21,704		—		—
Mortgage-backed and asset-backed securities		1,223		1,223		—		—
Agency bonds		299		299		—		—
Marketable securities		23,226		23,226		—		—
Deferred compensation plan investments		1,282		1,282		—		—
Assets at fair value	$	51,430	$	51,430	$	—	$	—
Liabilities:
Interest rate swap	$	240	$	—	$	240	$	—
Deferred compensation		873		873		—		—
Liabilities at fair value	$	1,113	$	873	$	240	$	—

The carrying values of financial instruments, including accounts receivable, unbilled receivables, and accounts payable approximate their fair values due to their short-term maturities.

We hold marketable securities that are investment grade and are classified as available-for-sale. The securities include corporate bonds, agency bonds, and mortgage and asset-backed securities that are carried at fair market value based on quoted market prices.

We hold trading securities as part of a rabbi trust to fund supplemental executive retirement plans and deferred income plans. The funds held are all managed by a third party and include fixed income funds, equity securities, and money market accounts, or other investments for which there is an active quoted market. The related deferred compensation liabilities are valued based on the underlying investment selections in each participant’s account.

The interest rate swap was valued based on forward curves observable in the market, using Level 2 inputs; see Note 12. The effectiveness of the interest rate swap is computed by comparing the present value of the cumulative change in the expected future cash flows of the variable leg of the swap and the present value of the cumulative change in the expected future variable interest payments designated in the hedging relationship.

Assets and liabilities that are measured at fair value on a non-recurring basis include long-lived assets, intangible assets, and goodwill. These items are recognized at fair value when they are considered to be other than temporarily impaired using significant unobservable inputs and are classified as Level 3.

The long-term debt, excluding leases, is reported at the borrowed amounts outstanding. The estimated fair value is based on a market approach using quoted market prices or current market rates for similar debt with approximately the same remaining maturities, where possible, and are classified as Level 2.

Our long-term debt, excluding leases, consisted of borrowings under our Senior Credit Facilities and 7.75% convertible senior notes; see Note 12. At March 31, 2015, the estimated fair value of our long-term debt, excluding leases, was approximately $116,000 versus a carrying value of $117,670. At December 31, 2014, the estimated fair value of the long-term debt, excluding leases, was approximately $123,000 versus a carrying value of $124,567.

There were no transfers in or out of Level 1, 2, or 3 during the three months ended March 31, 2015.