Summary of Significant Accounting Policies (Net Income Per Share) (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
Numerator
Net income	$ 53,027	$ (10,478)	$ (9,511)	$ (10,040)	$ 35,411	$ (9,953)	$ (3,650)	$ (7,760)	$ 22,998	$ 14,048	$ 17,127
Denominator for basic net income per share
Weighted-average common shares outstanding (in shares)									35,826	32,788	27,025
Dilutive effect of stock options and restricted awards (in shares)									1,606	2,219	2,224
Denominator for diluted net income per share (in shares)									37,432	35,007	29,249
Net income per share:
Basic (in dollars per share)	$ 1.46	$ (0.29)	$ (0.27)	$ (0.29)	$ 1.02	$ (0.29)	$ (0.11)	$ (0.27)	$ 0.64	$ 0.43	$ 0.63
Diluted (in dollars per share)	$ 1.40	$ (0.29)	$ (0.27)	$ (0.29)	$ 0.97	$ (0.29)	$ (0.11)	$ (0.27)	$ 0.61	$ 0.40	$ 0.59
Stock options and restricted stock units (in shares)									748	278	830