Quarterly Financial Data - Summary of Quarterly Financial Data (Detail) (USD $) In Thousands, except Per Share data, unless otherwise specified	3 Months Ended								12 Months Ended
	Dec. 31, 2012	Sep. 30, 2012	Jun. 30, 2012	Mar. 31, 2012	Dec. 31, 2011	Sep. 30, 2011	Jun. 30, 2011	Mar. 31, 2011	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Condensed Financial Statements, Captions [Line Items]
Revenue	$ 52,743	$ 46,839	$ 48,235	$ 48,461	$ 49,510	$ 47,619	$ 50,862	$ 49,720	$ 196,278	$ 197,711	$ 171,610
Gross profit	32,120	29,633	30,196	31,819	24,911	30,207	29,861	31,951	123,768	116,930	112,817
Total operating expenses	36,108	31,606	33,947	31,944	41,399	32,569	33,165	34,313	133,605	141,446	124,606
Net loss	$ (5,355)	$ (2,469)	$ (6,374)	$ (1,261)	$ (15,966)	$ (1,304)	$ (3,044)	$ (1,867)	$ (15,459)	$ (22,181)	$ (14,355)
Basic and diluted net loss per common share	$ (0.06)	$ (0.03)	$ (0.07)	$ (0.01)	$ (0.18)	$ (0.01)	$ (0.03)	$ (0.02)	$ (0.17)	$ (0.25)	$ (0.18)