Selected Quarterly Financial Data - Schedule of Selected Quarterly Financial Data (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
Quarterly Financial Information Disclosure [Abstract]
Total revenues	$ 50,151	$ 49,905	$ 48,611	$ 47,126	$ 47,689	$ 46,600	$ 43,375	$ 41,029	$ 195,793	$ 178,693	$ 145,763
Gross profit	31,499	31,740	30,460	29,900	30,346	29,365	26,735	25,574	123,599	112,020	90,471
Net loss	$ (8,549)	$ (8,829)	$ (9,310)	$ (8,165)	$ (12,090)	$ (12,109)	$ (14,630)	$ (17,324)	$ (34,853)	$ (56,153)	$ (75,371)
Basic and diluted net loss per share (dollars per share)	$ (0.11)	$ (0.12)	$ (0.12)	$ (0.11)	$ (0.17)	$ (0.17)	$ (0.21)	$ (0.25)	$ (0.46)	$ (0.79)	$ (1.12)