Marketable Securities and Fair Value Measurements - Schedule of the Fair Value of the Company's Financial Assets Measured at Fair Value on a Recurring Basis Based on the Three-Tier Value Hierarchy (Details) - Recurring - USD ($) $ in Thousands	Sep. 30, 2017	Dec. 31, 2016
Marketable securities and fair value measurements
Total	$ 604,437	$ 305,577
Cash equivalents
Marketable securities and fair value measurements
Money market funds and other funds	512,929	200,867
Commercial paper		5,640
Short-term investments
Marketable securities and fair value measurements
Investment securities	56,699	63,103
Restricted cash
Marketable securities and fair value measurements
Certificate of deposit	5,000	5,000
Long-term marketable securities
Marketable securities and fair value measurements
Investment securities	29,809	30,967
Level 1
Marketable securities and fair value measurements
Total	517,929	205,867
Level 1 | Cash equivalents
Marketable securities and fair value measurements
Money market funds and other funds	512,929	200,867
Commercial paper		0
Level 1 | Short-term investments
Marketable securities and fair value measurements
Investment securities	0	0
Level 1 | Restricted cash
Marketable securities and fair value measurements
Certificate of deposit	5,000	5,000
Level 1 | Long-term marketable securities
Marketable securities and fair value measurements
Investment securities	0	0
Level 2
Marketable securities and fair value measurements
Total	86,508	99,710
Level 2 | Cash equivalents
Marketable securities and fair value measurements
Money market funds and other funds	0	0
Commercial paper		5,640
Level 2 | Short-term investments
Marketable securities and fair value measurements
Investment securities	56,699	63,103
Level 2 | Restricted cash
Marketable securities and fair value measurements
Certificate of deposit	0	0
Level 2 | Long-term marketable securities
Marketable securities and fair value measurements
Investment securities	29,809	30,967
Level 3
Marketable securities and fair value measurements
Total	0	0
Level 3 | Cash equivalents
Marketable securities and fair value measurements
Money market funds and other funds	0	0
Commercial paper		0
Level 3 | Short-term investments
Marketable securities and fair value measurements
Investment securities	0	0
Level 3 | Restricted cash
Marketable securities and fair value measurements
Certificate of deposit	0	0
Level 3 | Long-term marketable securities
Marketable securities and fair value measurements
Investment securities	$ 0	$ 0