Segment Reporting (Detail) - Revenue By Location (USD $) In Thousands, 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
United States (in dollars)	$ 67,747	$ 65,407	$ 64,293	$ 61,888	$ 60,275	$ 58,554	$ 57,481	$ 61,194	$ 259,335	$ 237,504	$ 197,688
Total revenue (in dollars)	67,747	65,407	64,293	61,888	60,275	58,554	57,481	61,194	259,335	237,504	197,688
Total revenue									100.00%	100.00%	100.00%
United States
United States (in dollars)									166,593	145,310	111,419
United States									64.00%	61.00%	56.00%
Total revenue (in dollars)									166,593	145,310	111,419
Japan
United States (in dollars)									36,849	39,465	40,484
Other foreign country									14.00%	17.00%	20.00%
Total revenue (in dollars)									36,849	39,465	40,484
Other
United States (in dollars)									55,893	52,729	45,785
Other foreign country									22.00%	22.00%	24.00%
Total revenue (in dollars)									$ 55,893	$ 52,729	$ 45,785