Investments - Summary of Short-Term Investments (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015
Investment [Line Items]
Maturity weighted average period, in years (less than)	2 years
Amortized cost	$ 61,236	$ 98,184
Unrealized Gains	12	22
Unrealized Losses	(78)	(103)
Estimated fair value	$ 61,170	$ 98,103
Corporate debt securities
Investment [Line Items]
Maturity (or less) (in years)	2 years	2 years
Amortized cost	$ 49,185	$ 81,054
Unrealized Gains	12	16
Unrealized Losses	(77)	(103)
Estimated fair value	$ 49,120	$ 80,967
Certificates of deposit
Investment [Line Items]
Maturity (or less) (in years)	1 year	2 years
Amortized cost	$ 9,291	$ 13,640
Unrealized Gains	0	0
Unrealized Losses	0	0
Estimated fair value	$ 9,291	$ 13,640
Commercial paper
Investment [Line Items]
Maturity (or less) (in years)	1 year	1 year
Amortized cost	$ 1,247	$ 3,490
Unrealized Gains	0	6
Unrealized Losses	0	0
Estimated fair value	$ 1,247	$ 3,496
U.S. treasury securities
Investment [Line Items]
Maturity (or less) (in years)	1 year
Amortized cost	$ 1,001
Unrealized Gains	0
Unrealized Losses	(1)
Estimated fair value	$ 1,000
Debt securities of U.S. government-sponsored agencies
Investment [Line Items]
Maturity (or less) (in years)	1 year
Amortized cost	$ 512
Unrealized Gains	0
Unrealized Losses	0
Estimated fair value	$ 512