Fair Value Measurements - Assets and Liabilities Measured at Fair Value on Recurring Basis (Detail) - USD ($)	3 Months Ended		9 Months Ended
	Sep. 30, 2016	Sep. 30, 2015	Sep. 30, 2016	Sep. 30, 2015	Dec. 31, 2015
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Change in fair value of acquisition contingencies	$ 600,000	$ 0	$ 600,000.0	$ 0
Assets:
Total assets measured at fair value	133,450,000		133,450,000		$ 133,147,000
Liabilities:
Total liabilities measured at fair value	5,075,000		5,075,000		5,516,000
Money Market Funds [Member]
Assets:
Cash Equivalents, at Carrying Value	133,450,000		133,450,000		133,147,000
Contingent consideration [Member]
Liabilities:
Total liabilities measured at fair value	5,075,000		5,075,000		5,516,000
Level 1 [Member]
Assets:
Total assets measured at fair value	133,450,000		133,450,000		133,147,000
Liabilities:
Total liabilities measured at fair value	0		0		0
Level 1 [Member] | Money Market Funds [Member]
Assets:
Cash Equivalents, at Carrying Value	133,450,000		133,450,000		133,147,000
Level 1 [Member] | Contingent consideration [Member]
Liabilities:
Total liabilities measured at fair value	0		0		0
Level 2 [Member]
Assets:
Total assets measured at fair value	0		0		0
Liabilities:
Total liabilities measured at fair value	0		0		0
Level 2 [Member] | Money Market Funds [Member]
Assets:
Cash Equivalents, at Carrying Value	0		0		0
Level 2 [Member] | Contingent consideration [Member]
Liabilities:
Total liabilities measured at fair value	0		0		0
Level 3 [Member]
Assets:
Total assets measured at fair value	0		0		0
Liabilities:
Total liabilities measured at fair value	5,075,000		5,075,000		5,516,000
Level 3 [Member] | Money Market Funds [Member]
Assets:
Cash Equivalents, at Carrying Value	0		0		0
Level 3 [Member] | Contingent consideration [Member]
Liabilities:
Total liabilities measured at fair value	$ 5,075,000		$ 5,075,000		$ 5,516,000