Cash and Investments in Marketable Securities

12 Months Ended

Dec. 31, 2016

Fair Value Disclosures [Abstract]

Cash and Investments in Marketable Securities

Note 2 — Cash and Investments in Marketable Securities

Cash and investments in marketable securities, including cash equivalents and restricted cash, are as follows (in thousands).

	Estimated Fair Value at
	December 31, 2016		December 31, 2015
Cash and cash equivalents	$	59,640	$	55,570
Short-term investments		329,462		253,374
Total cash and investments in marketable securities	$	389,102	$	308,944

We invest in liquid, high quality debt securities. Our investments in debt securities are subject to interest rate risk. To minimize the exposure due to an adverse shift in interest rates, we invest in securities with maturities of two years or less and maintain a weighted average maturity of one year or less. As December 31, 2016 and 2015, all of our investments had maturities of one year or less.

Gross unrealized gains and losses were not significant at either December 31, 2016 or 2015. During the years ended December 31, 2016, 2015 and 2014, we sold available-for-sale securities totaling $5.0 million, $42.5 million, and $21.7 million, respectively, and realized gains and losses were not significant in any of those periods.

Under the terms of our 7.75% senior secured notes due October 2020, we are required to maintain a minimum cash and investments in marketable securities balance of $60.0 million.  

Our portfolio of cash and investments in marketable securities includes (in thousands):

			Estimated Fair Value at
	Fair Value Hierarchy Level		December 31, 2016		December 31, 2015
Corporate commercial paper		2	$	160,920	$	61,150
Corporate notes and bonds		2		156,044		181,969
Obligations of U.S. government agencies		2		13,749		7,325
Available-for-sale investments				330,713		250,444
Money market funds		1		51,104		53,728
Certificate of deposit	N/A			2,930		2,930
Cash	N/A			4,355		1,842
Total cash and investments in marketable securities			$	389,102	$	308,944

Level 1 — Quoted prices in active markets for identical assets or liabilities.

Level 2 — Inputs other than Level 1 that are observable, either directly or indirectly, such as quoted prices for similar assets or liabilities; quoted prices in markets that are not active; or other inputs that are observable or can be corroborated by observable market data for substantially the full term of the assets or liabilities.

Level 3 — Unobservable inputs that are supported by little or no market activity and that are significant to the fair value of the assets or liabilities.

All of our investments are categorized as Level 1 or Level 2, as explained in the table above. During the years ended December 31, 2016, 2015 and 2014 there were no transfers between Level 1 and Level 2 of the fair value hierarchy.

At December 31, 2016 and 2015, we had letter of credit arrangements in favor of a landlord and certain vendors totaling $2.4 million. These letters of credit are secured by investments of similar amounts.