Selected Quarterly Financial Data - (unaudited) (Detail) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2014	Sep. 30, 2014	Jun. 30, 2014	Mar. 31, 2014	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Revenue:
Consumer revenue	$ 148,289	$ 144,648	$ 138,329	$ 128,201	$ 122,745	$ 116,115	$ 109,338	$ 100,995	$ 559,467	$ 449,193	$ 340,121
Enterprise revenue	7,863	7,304	6,628	6,207	6,941	6,916	6,375	6,591	28,002	26,823	29,537
Total revenue	156,152	151,952	144,957	134,408	129,686	123,031	115,713	107,586	587,469	476,016	369,658
Gross profit	122,266	117,964	110,031	99,852	98,939	92,704	86,322	77,629	450,113	355,594	269,593
Income (loss) from operations	16,864	(87,350)	865	(15,132)	6,299	9,533	(2,561)	(7,205)	(84,753)	6,066	17,181
Net income (loss)	$ 22,780	$ (65,145)	$ 520	$ (9,158)	$ 2,838	$ 5,450	$ (1,498)	$ (4,295)	$ (51,003)	$ 2,495	$ 54,455
Basic net income (loss) per share (USD per share)	$ 0.24	$ (0.68)	$ 0.01	$ (0.10)	$ 0.03	$ 0.06	$ (0.02)	$ (0.05)	$ (0.54)	$ 0.03	$ 0.61
Diluted net income (loss) per share (USD per share)	$ 0.23	$ (0.68)	$ 0.01	$ (0.10)	$ 0.03	$ 0.06	$ (0.02)	$ (0.05)	$ (0.54)	$ 0.03	$ 0.57