Goodwill and Acquired Intangible Assets - Additional Information (Detail) (USD $)	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Finite-Lived Intangible Assets [Line Items]
Goodwill acquired	$ 34,972,000
Intangible assets acquired	10,668,000
Gross carrying amount of goodwill	34,972,000	0
Goodwill impairments	0	0	0
Amortization expense related to acquired intangible assets	1,269,000	0	0
Acquired intangible assets	$ 9,399,000	$ 0
Minimum [Member]
Finite-Lived Intangible Assets [Line Items]
Estimated useful life	7 years
Maximum [Member]
Finite-Lived Intangible Assets [Line Items]
Estimated useful life	10 years