Description of Business and Summary of Significant Accounting Policies - Income Per share (Detail) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2014	Sep. 30, 2014	Jun. 30, 2014	Mar. 31, 2014	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Earnings Per Share [Abstract]
Net Income(loss)	$ 38,899	$ 26,691	$ 41,389	$ 4,532	$ 62,213	$ 15,130	$ 23,039	$ 20,653	$ 111,511	$ 121,035	$ 113,483
Net Income(loss), shares									51,241	50,861	51,174
Net Income(loss), per shares	$ 0.76	$ 0.52	$ 0.81	$ 0.09	$ 1.22	$ 0.30	$ 0.45	$ 0.41	$ 2.18	$ 2.38	$ 2.22
Effect of dilutive stock-based compensation									371	487	591
Effect of convertible notes										4,532	6,304
Effect of common stock warrants											4,741
Net Income (loss)- Assuming dilution									$ 111,511	$ 121,035	$ 113,483
Net Income (loss)- Assuming dilution, shares									51,612	55,880	62,810
Net Income (loss)- Assuming dilution, per shares	$ 0.75	$ 0.52	$ 0.80	$ 0.09	$ 1.21	$ 0.25	$ 0.38	$ 0.32	$ 2.16	$ 2.17	$ 1.81