2. SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES

Use of Estimates in Preparation of Financial Statements. The preparation of the accompanying Financial Statements in conformity with GAAP requires management to make estimates and assumptions that affect the reported amounts of assets and liabilities and disclosure of contingent assets and liabilities at the date of our Financial Statements, and the reported amounts of revenues and expenses during the reporting periods. Actual results could differ from those estimates.

Reclassifications. Certain December 31, 2015 amounts have been reclassified to conform to the March 31, 2016 presentation, which are discussed further in the Accounting Pronouncements Adopted section below.

Cash and Cash Equivalents. We consider all highly liquid investments with original maturities of three months or less at the date of the purchase to be cash equivalents. As of March 31, 2016 and December 31, 2015, our cash equivalents consist primarily of institutional money market funds, commercial paper, and time deposits held at major banks.

As of March 31, 2016 and December 31, 2015, we had $4.6 million and $5.0 million, respectively, of restricted cash that serves to collateralize outstanding letters of credit. This restricted cash is included in cash and cash equivalents in our Condensed Consolidated Balance Sheets (“Balance Sheets” or “Balance Sheet”).

Short-term Investments and Other Financial Instruments. Our financial instruments as of March 31, 2016 and December 31, 2015 include cash and cash equivalents, short-term investments, accounts receivable, accounts payable, and debt. Because of their short maturities, the carrying amounts of cash equivalents, accounts receivable, and accounts payable approximate their fair value.

Our short-term investments and certain of our cash equivalents are considered “available-for-sale” and are reported at fair value in our Balance Sheets, with unrealized gains and losses, net of the related income tax effect, excluded from earnings and reported in a separate component of stockholders’ equity. Realized and unrealized gains and losses were not material in any period presented.

Primarily all short-term investments held by us as of March 31, 2016 and December 31, 2015 have contractual maturities of less than two years from the time of acquisition. Our short-term investments as of March 31, 2016 and December 31, 2015 consisted almost entirely of fixed income securities. Proceeds from the sale/maturity of short-term investments for the first quarters of 2016 and 2015 were $30.1 million and $49.5 million, respectively.

The following table represents the fair value hierarchy based upon three levels of inputs, of which Levels 1 and 2 are considered observable and Level 3 is unobservable, for our financial assets and liabilities measured at fair value (in thousands):

	March 31, 2016						December 31, 2015
	Level 1			Level 2		Total	Level 1		Level 2		Total
Assets:
Cash equivalents:
Money market funds	$	79,156	$	—	$	79,156	$	35,730	$	—	$	35,730
Commercial paper		—		—		—		—		63,890		63,890
Short-term investments:
Corporate debt securities		—		56,623		56,623		—		31,253		31,253
Corporate equity securities		3,024		—		3,024		—		—		—
Municipal bonds		—		2,763		2,763		—		2,763		2,763
U.S. government agency bonds		—		23,245		23,245		—		16,201		16,201
Asset-backed securities		—		9,841		9,841		—		11,443		11,443
Total	$	82,180	$	92,472	$	174,652	$	35,730	$	125,550	$	161,280

Valuation inputs used to measure the fair values of our money market funds and corporate equity securities were derived from quoted market prices. The fair values of all other financial instruments are based upon pricing provided by third-party pricing services. These prices were derived from observable market inputs.

We have chosen not to measure our debt at fair value, with changes recognized in earnings each reporting period. The following table indicates the carrying value and estimated fair value of our debt as of the indicated periods (in thousands):

	March 31, 2016				December 31, 2015
	Carrying Value		Fair Value		Carrying Value		Fair Value
Credit agreement (carrying value including current maturities)	$	140,625	$	140,625	$	142,500	$	142,500
2010 Convertible debt (par value)		110,000		218,878		150,000		237,900
2016 Convertible debt (par value)		230,000		246,100		—		—

The fair value for our credit agreement was estimated using a discounted cash flow methodology, while the fair value for our convertible debt was estimated based upon quoted market prices or recent sales activity, both of which are considered Level 2 inputs. See Note 4 for additional discussion regarding our convertible debt.

Accounting Pronouncements Adopted. In April 2015, the Financial Accounting Standards Board (“FASB”) issued Accounting Standards Update (“ASU”) 2015-03, Interest-Imputation of Interest (Subtopic 835-30). This ASU requires that debt issuance costs related to a recognized debt liability be presented in the balance sheet as a reduction from the carrying amount of that debt liability, consistent with debt discounts. This ASU is effective in fiscal years beginning after December 15, 2015 and must be applied retrospectively. We adopted this ASU retrospectively on January 1, 2016, which resulted in the reclassification of $5.4 million of debt issuance costs from other assets to long-term debt on our December 31, 2015 Balance Sheet.

In November 2015, the FASB issued ASU 2015-17, Income Taxes (Topic 740), requiring that all deferred tax liabilities and assets be classified as noncurrent. Prior guidance required us to record deferred tax balances as either current or non-current in accordance with the classification of the underlying attributes. This ASU is effective in fiscal years beginning after December 15, 2016, with early adoption permitted and may be applied either prospectively to all deferred tax liabilities and assets or retrospectively to all periods presented. We adopted this ASU retrospectively on January 1, 2016, which resulted in a decrease of $18.1 million in current deferred income tax assets, an increase in non-current deferred income tax assets of $9.1 million and a decrease in non-current deferred income tax liabilities of $9.0 million on our December 31, 2015 Balance Sheet.

Accounting Pronouncement Issued But Not Yet Effective. The FASB has issued ASU 2014-09, Revenue from Contracts with Customers (Topic 606). This ASU is a single comprehensive model which supersedes nearly all existing revenue recognition guidance under U.S. GAAP. Under the new guidance, revenue is recognized when promised goods or services are transferred to customers in an amount that reflects the consideration that is expected to be received for those goods or services. The ASU also requires additional disclosure about the nature, amount, timing, and uncertainty of revenue and cash flows arising from customer contracts, including significant judgments and changes in judgments and assets recognized from costs incurred to obtain or fulfill a contract. In August 2015, the FASB issued ASU 2015-14 Revenue from Contracts with Customers (Topic 606): Deferral of the Effective Date which defers the effective date of ASU 2014-09 for one year. The updated accounting guidance is now effective for annual and interim reporting periods in fiscal years beginning after December 15, 2017. Early adoption is permitted. An entity may choose to adopt this ASU either retrospectively or through a cumulative effect adjustment as of the start of the first period for which it applies the standard. We are currently in the process of evaluating the impact that this new guidance will have on our Financial Statements and our method of adoption.

In February 2016, the FASB issued ASU 2016-02, Leases (Topic 842). This ASU requires lessees to recognize a lease liability and a right-to-use asset for all leases, including operating leases, with a term greater than twelve months on its balance sheet. This ASU is effective in annual and interim periods in fiscal years beginning after December 15, 2018, with early adoption permitted, and requires a modified retrospective transition method. We are currently in the process of evaluating the impact that this new guidance will have on our Financial Statements.

In March 2016, the FASB issued ASU 2016-09, Compensation – Stock Compensation (Topic 718). This ASU simplifies several aspects of the accounting for share-based payment transactions, including the income tax consequences, classification of awards as either equity or liabilities, and classification on the statement of cash flows. This ASU is effective for fiscal years beginning after December 15, 2016, with early adoption permitted. The methods of adoption for this ASU vary by amendment. We are currently in the process of evaluating the impact that this new guidance will have on our Financial Statements.