Description of Business and Summary of Significant Accounting Policies - Income Loss Per share (Detail) (USD $) In Thousands, except Per Share data, 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
Earnings Per Share [Abstract]
Net Income(loss)	$ 62,213	$ 15,130	$ 23,039	$ 20,653	$ 30,162	$ 18,031	$ 11,510	$ 53,780	$ 121,035	$ 113,483	$ (26,644)
Net Income(loss), shares									50,861	51,174	47,602
Net Income(loss), per shares	$ 1.22	$ 0.30	$ 0.45	$ 0.41	$ 0.60	$ 0.36	$ 0.22	$ 1.03	$ 2.38	$ 2.22	$ (0.56)
Effect of dilutive stock-based compensation									487	591
Effect of convertible notes									4,532	6,304
Effect of common stock warrants										4,741
Net Income (loss)- Assuming dilution									$ 121,035	$ 113,483	$ (26,644)
Net Income (loss)- Assuming dilution, shares									55,880	62,810	47,602
Net Income (loss)- Assuming dilution, per shares	$ 1.21	$ 0.25	$ 0.38	$ 0.32	$ 0.48	$ 0.30	$ 0.18	$ 0.81	$ 2.17	$ 1.81	$ (0.56)