Investments and Fair Value Measurements - Summary of Investments in Fixed Income Securities (Details) - USD ($) $ in Thousands	Dec. 31, 2016	Dec. 31, 2015
Schedule Of Available For Sale Securities [Line Items]
Amortized Cost	$ 52,613	$ 67,930
Unrealized Gains		1
Unrealized Losses	(19)	(116)
Estimated Fair Value	52,594	67,815
Cash Equivalents [Member] \| Money Market Funds [Member]
Schedule Of Available For Sale Securities [Line Items]
Amortized Cost	1,549	12,799
Unrealized Gains		0
Unrealized Losses		0
Estimated Fair Value	1,549	12,799
Cash Equivalents [Member] \| Commercial Paper [Member]
Schedule Of Available For Sale Securities [Line Items]
Amortized Cost		5,949
Unrealized Gains		0
Unrealized Losses		0
Estimated Fair Value		5,949
Cash Equivalents [Member] \| U.S. Government Agency Securities [Member]
Schedule Of Available For Sale Securities [Line Items]
Amortized Cost		3,049
Unrealized Gains		0
Unrealized Losses		0
Estimated Fair Value		3,049
Short-term Investments [Member] \| Certificates of Deposit [Member]
Schedule Of Available For Sale Securities [Line Items]
Amortized Cost	3,049	3,374
Unrealized Gains		0
Unrealized Losses	(2)	0
Estimated Fair Value	3,047	3,374
Short-term Investments [Member] \| Commercial Paper [Member]
Schedule Of Available For Sale Securities [Line Items]
Amortized Cost	21,248	3,598
Unrealized Gains		0
Unrealized Losses		0
Estimated Fair Value	21,248	3,598
Short-term Investments [Member] \| U.S. Government Securities [Member]
Schedule Of Available For Sale Securities [Line Items]
Amortized Cost	19,267	13,678
Unrealized Gains		0
Unrealized Losses	(9)	(30)
Estimated Fair Value	19,258	13,648
Short-term Investments [Member] \| U.S. Government Agency Securities [Member]
Schedule Of Available For Sale Securities [Line Items]
Amortized Cost	5,000	5,653
Unrealized Gains		1
Unrealized Losses	(6)	(4)
Estimated Fair Value	4,994	5,650
Long-term investments [Member] \| Certificates of Deposit [Member]
Schedule Of Available For Sale Securities [Line Items]
Amortized Cost		3,049
Unrealized Gains		0
Unrealized Losses		0
Estimated Fair Value		3,049
Long-term investments [Member] \| U.S. Government Securities [Member]
Schedule Of Available For Sale Securities [Line Items]
Amortized Cost	2,500	11,780
Unrealized Gains		0
Unrealized Losses	(2)	(52)
Estimated Fair Value	$ 2,498	11,728
Long-term investments [Member] \| U.S. Government Agency Securities [Member]
Schedule Of Available For Sale Securities [Line Items]
Amortized Cost		5,001
Unrealized Gains		0
Unrealized Losses		(30)
Estimated Fair Value		$ 4,971

Amount of investment in debt and equity securities categorized neither as held-to-maturity nor trading.

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-Publisher FASB
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