Cash and Investments (Tables)

12 Months Ended

Dec. 31, 2016

Cash And Cash Equivalents [Abstract]

Schedule of Cash and Investments

Cash and investments consist of the following (in thousands):

	December31, 2016		December 31, 2015
Cash and cash equivalents:
Cash	$	123,382	$	162,495
Money market funds		439,330		362,587
Commercial paper		235,783		160,151
Corporate bonds		33,985		16,995
U.S. government and government agency debt securities		19,987		39,989
Total cash and cash equivalents	$	852,467	$	742,217
Marketable securities:
U.S. government and government agency debt securities	$	—	$	144,986
Corporate debt securities		—		100,047
Total	$	—	$	245,033

Summary of Available-for-Sale Investments

The following tables summarize our amortized cost, gross unrealized gains and losses and fair value of our available-for-sale investments in marketable securities (in thousands) as of December 31, 2015 (we had no available-for-sale investments in marketable securities as of December 31, 2016):

	December 31, 2015
			Gross		Gross
	Amortized		Unrealized		Unrealized			Aggregate
	Cost		Gains		Losses			Fair Value
U.S. government and government agency debt securities	$	145,066	$	—	$	(80	)	$	144,986
Corporate debt securities		100,093		12		(58	)		100,047
Total	$	245,159	$	12	$	(138	)	$	245,033

Fair Value of Available-for-Sale Marketable Securities by Contractual Maturities

The estimated fair value of available-for-sale marketable securities as of December 31, 2015, classified by their contractual maturities was as follows (in thousands):

	December 31, 2015
Due within one year	$	245,033
After one year through three years		—
Total	$	245,033

Schedule of Unrealized Losses on Marketable Securities

Changes in market interest rates and bond yields cause certain of our investments to fall below their cost basis, resulting in unrealized losses. As of December 31, 2016, we had unrealized losses of $27 thousand related to investments that had a fair value of $34.0 million. As of December 31, 2015, we had unrealized losses of $0.1 million related to investments that had a fair value of $199.1 million. None of these investments were in a material continuous unrealized loss position for more than 12 months.

	December 31, 2016					December 31, 2015
	Fair Value		Unrealized loss			Fair Value		Unrealized loss
U.S. government and government agency debt securities	$	—	$	—		$	137,485	$	(80	)
Corporate debt securities		33,984		(27	)		61,622		(58	)
Total	$	33,984	$	(27	)	$	199,107	$	(138	)