Quarterly Financial Data (Details) (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
Quarterly Financial Data [Abstract]
Revenue	$ 76,702		$ 78,628		$ 78,303		$ 79,195		$ 74,904		$ 75,058		$ 55,918		$ 52,905		$ 312,828		$ 258,785		$ 146,982
Gross margin	31,300		33,843		33,025		33,451		31,714		30,717		22,244		21,145		131,619		105,820		52,970
Net income (loss)	$ 23,201		$ 9,806		$ 13,178		$ 3,606		$ 991		$ 17,917		$ 2,126		$ 10,374		$ 49,791		$ 31,408		$ (43,465)
Earnings (loss) per common share:
Basic (in dollars per share)	$ 0.48	[1]	$ 0.20	[1]	$ 0.27	[1]	$ 0.08	[1]	$ 0.02	[1]	$ 0.38	[1]	$ 0.05	[1]	$ 0.15	[1]	$ 1.03	[1]	$ 0.60	[1]	$ (1.94)
Diluted (in dollars per share)	$ 0.44	[1]	$ 0.19	[1]	$ 0.25	[1]	$ 0.07	[1]	$ 0.02	[1]	$ 0.35	[1]	$ 0.04	[1]	$ 0.13	[1]	$ 0.97	[1]	$ 0.56	[1]	$ (1.94)

[1] The sum of the quarterly earnings per share applicable to common stockholders (basic and diluted) may not agree to the earnings per share for the year due to the timing of common stock issuances.