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, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Earnings Per Share [Abstract]
Net Income(loss)	$ 48,096	$ 33,593	$ 51,331	$ 26,346	$ 38,899	$ 26,691	$ 41,389	$ 4,532	$ 159,366	$ 111,511	$ 121,035
Net Income(loss), shares									51,009	51,241	50,861
Net Income(loss), per shares	$ 0.94	$ 0.66	$ 1.01	$ 0.52	$ 0.76	$ 0.52	$ 0.81	$ 0.09	$ 3.12	$ 2.18	$ 2.38
Effect of dilutive stock-based compensation									303	371	487
Effect of convertible notes											4,532
Net Income (loss)- Assuming dilution									$ 159,366	$ 111,511	$ 121,035
Net Income (loss)- Assuming dilution, shares									51,312	51,612	55,880
Net Income (loss)- Assuming dilution, per shares	$ 0.94	$ 0.66	$ 1.00	$ 0.51	$ 0.75	$ 0.52	$ 0.80	$ 0.09	$ 3.11	$ 2.16	$ 2.17