Selected Quarterly Financial Data - (unaudited) (Detail) (USD $) In Thousands, except Per Share data, unless otherwise specified	3 Months Ended								12 Months Ended
	Dec. 31, 2014	Sep. 30, 2014	Jun. 30, 2014	Mar. 31, 2014	Dec. 31, 2013	Sep. 30, 2013	Jun. 30, 2013	Mar. 31, 2013	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Revenue:
Consumer revenue	$ 122,745	$ 116,115	$ 109,338	$ 100,995	$ 94,068	$ 88,386	$ 82,574	$ 75,094	$ 449,193	$ 340,121	$ 254,678
Enterprise revenue	6,941	6,916	6,375	6,591	8,237	7,353	6,946	7,001	26,823	29,537	21,750
Total revenue	129,686	123,031	115,713	107,586	102,305	95,739	89,520	82,095	476,016	369,658	276,428
Gross profit	98,939	92,704	86,322	77,629	76,110	70,852	64,326	58,305	355,594	269,593	196,512
Income (loss) from operations	6,299	9,533	(2,561)	(7,205)	15,293	6,736	(1,404)	(3,444)	6,066	17,181	13,093
Net income (loss)	$ 2,838	$ 5,450	$ (1,498)	$ (4,295)	$ 52,976	$ 6,466	$ (1,445)	$ (3,542)	$ 2,495	$ 54,455	$ 23,503
Basic net income (loss) per share (in usd per share)	$ 0.03	$ 0.06	$ (0.02)	$ (0.05)	$ 0.58	$ 0.07	$ (0.02)	$ (0.04)	$ 0.03	$ 0.61	$ 0.18
Diluted net income (loss) per share (in usd per share)	$ 0.03	$ 0.06	$ (0.02)	$ (0.05)	$ 0.54	$ 0.07	$ (0.02)	$ (0.04)	$ 0.03	$ 0.57	$ 0.09