Fair Value Measurements (Tables)

6 Months Ended

Jun. 30, 2018

Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]

Assets Measured at Fair Value on Recurring Basis

The following table presents our fair value hierarchy for our assets measured at fair value on a recurring basis at June 30, 2018 (in thousands): 

	Level 1		Level 2		Total
Cash equivalents:
Money market funds	$	176,304	$	—	$	176,304
Commercial paper	—		173,604		173,604
Corporate notes and bonds	—		6,598		6,598
Short-term investments:
Commercial paper	—		253,518		253,518
Corporate notes and bonds	—		678,619		678,619
Certificates of deposit	—		29,844		29,844
U.S. government agency securities	—		82,831		82,831
Long-term investments:
Corporate notes and bonds	—		272,060		272,060
Certificates of deposit	—		2,900		2,900
U.S. government agency securities	—		29,669		29,669
Total	$	176,304	$	1,529,643	$	1,705,947

The following table presents our fair value hierarchy for our assets measured at fair value on a recurring basis at December 31, 2017 (in thousands): 

	Level 1		Level 2		Total
Cash equivalents:
Money market funds	$	282,507	$	—	$	282,507
Commercial paper	—		100,456		100,456
Corporate notes and bonds	—		50,437		50,437
Short-term investments:
Commercial paper	—		258,344		258,344
Corporate notes and bonds	—		688,316		688,316
Certificates of deposit	—		17,950		17,950
U.S. government agency securities	—		67,476		67,476
Marketable equity securities	20,717		—		20,717
Long-term investments:
Corporate notes and bonds	—		314,928		314,928
Certificates of deposit	—		15,134		15,134
U.S. government agency securities	—		61,380		61,380
Total	$	303,224	$	1,574,421	$	1,877,645