Summary of Significant Accounting Policies - Summary of Assets and Liabilities Measured at Fair Value on Recurring Basis (Detail) - Fair Value, Measurements, Recurring [Member] - USD ($) $ in Thousands		Mar. 31, 2016	Dec. 31, 2015
Assets:
Cash Equivalents		$ 29,549	$ 23,125
Repurchase Agreements			20,000
Investments:
Total assets		139,599	174,274
Fair Value, Inputs, Level 2 [Member]
Assets:
Cash Equivalents		1,753	11,952
Repurchase Agreements			20,000
Investments:
Total assets		111,803	163,101
Not Subject to Leveling [Member]
Assets:
Cash Equivalents	[1]	27,796	11,173
Investments:
Total assets	[1]	27,796	11,173
Commercial Paper [Member]
Investments:
Investments		56,020	64,820
Commercial Paper [Member] | Fair Value, Inputs, Level 2 [Member]
Investments:
Investments		56,020	64,820
Corporate Bonds [Member]
Investments:
Investments		26,972	46,490
Corporate Bonds [Member] | Fair Value, Inputs, Level 2 [Member]
Investments:
Investments		26,972	46,490
Government Securities [Member]
Investments:
Investments		15,044	15,819
Government Securities [Member] | Fair Value, Inputs, Level 2 [Member]
Investments:
Investments		15,044	15,819
Treasury Bonds [Member]
Investments:
Investments		12,014	4,020
Treasury Bonds [Member] | Fair Value, Inputs, Level 2 [Member]
Investments:
Investments		$ 12,014	$ 4,020

[1] Certain cash equivalents and investments that are valued using the net asset value per share (or its equivalent) practical expedient have not been classified in the fair value hierarchy.