Fair Value Measurements - Assets and Liabilities Measured at Fair Value on Recurring Basis (Detail) - USD ($) $ in Thousands	Jun. 30, 2017	Dec. 31, 2016
Assets:
Total assets measured at fair value	$ 130,820	$ 133,540
Liabilities:
Total liabilities measured at fair value	4,691	5,175
Money Market Funds [Member]
Assets:
Cash Equivalents, at Carrying Value	130,820	133,540
Contingent consideration [Member]
Liabilities:
Total liabilities measured at fair value	4,691	5,175
Level 1 [Member]
Assets:
Total assets measured at fair value	130,820	133,540
Liabilities:
Total liabilities measured at fair value	0	0
Level 1 [Member] | Money Market Funds [Member]
Assets:
Cash Equivalents, at Carrying Value	130,820	133,540
Level 1 [Member] | Contingent consideration [Member]
Liabilities:
Total liabilities measured at fair value	0	0
Level 2 [Member]
Assets:
Total assets measured at fair value	0	0
Liabilities:
Total liabilities measured at fair value	0	0
Level 2 [Member] | Money Market Funds [Member]
Assets:
Cash Equivalents, at Carrying Value	0	0
Level 2 [Member] | Contingent consideration [Member]
Liabilities:
Total liabilities measured at fair value	0	0
Level 3 [Member]
Assets:
Total assets measured at fair value	0	0
Liabilities:
Total liabilities measured at fair value	4,691	5,175
Level 3 [Member] | Money Market Funds [Member]
Assets:
Cash Equivalents, at Carrying Value	0	0
Level 3 [Member] | Contingent consideration [Member]
Liabilities:
Total liabilities measured at fair value	$ 4,691	$ 5,175