Fair Value Measurements - Assets and Liabilities Measured at Fair Value on Recurring Basis (Detail) - USD ($)	3 Months Ended
	Mar. 31, 2017	Dec. 31, 2016
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Change in fair value of acquisition contingencies	$ 0
Assets:
Total assets measured at fair value	130,653,000	$ 133,540,000
Liabilities:
Total liabilities measured at fair value	4,689,000	5,175,000
Money Market Funds [Member]
Assets:
Cash Equivalents, at Carrying Value	130,653,000	133,540,000
Contingent consideration [Member]
Liabilities:
Total liabilities measured at fair value	4,689,000	5,175,000
Level 1 [Member]
Assets:
Total assets measured at fair value	130,653,000	133,540,000
Liabilities:
Total liabilities measured at fair value	0	0
Level 1 [Member] | Money Market Funds [Member]
Assets:
Cash Equivalents, at Carrying Value	130,653,000	133,540,000
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	4,689,000	5,175,000
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	$ 4,689,000	$ 5,175,000