Fair Value Measurements - Summary of Fair Value of Financial Assets and Liabilities that are Measured at Fair Value and the Classification by Level of Input within Fair Value Hierarchy (Detail) - USD ($) $ in Thousands	Jun. 30, 2016	Dec. 31, 2015
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total cash and cash equivalents	$ 58,519	$ 91,060
Total investments	53,617	59,310
Total cash, cash equivalents, and investments	112,136	150,370
Level 1
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total cash and cash equivalents	55,621	91,060
Total investments	0	0
Total cash, cash equivalents, and investments	55,621	91,060
Level 2
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total cash and cash equivalents	2,898
Total investments	53,617	59,310
Total cash, cash equivalents, and investments	56,515	59,310
Level 3
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total investments	0	0
Total cash, cash equivalents, and investments	0	0
Certificates of deposit
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total investments	14,612	18,355
Certificates of deposit | Level 2
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total investments	14,612	18,355
Commercial paper
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total investments	6,494	5,966
Commercial paper | Level 2
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total investments	6,494	5,966
Corporate bonds
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total investments	27,987	32,995
Corporate bonds | Level 2
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total investments	27,987	32,995
Government agencies
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total investments	4,524	1,994
Government agencies | Level 2
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total investments	4,524	1,994
Cash and money market accounts
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total cash and cash equivalents	55,621	91,060
Cash and money market accounts | Level 1
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total cash and cash equivalents	55,621	$ 91,060
Commercial paper
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total cash and cash equivalents	1,498
Commercial paper | Level 2
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total cash and cash equivalents	1,498
Government agencies
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total cash and cash equivalents	1,400
Government agencies | Level 2
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total cash and cash equivalents	$ 1,400