Calculation of Basic and Diluted Net Income Per Share (Detail) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Basic net income per share:
Net income applicable to common stockholders	$ 4,664	$ 18,947	$ 57,837	$ 62,066
Weighted average common shares outstanding	56,798	58,994	57,486	59,675
Basic net income per share	$ 0.08	$ 0.32	$ 1.01	$ 1.04
Diluted net income per share:
Net income applicable to common stockholders	$ 4,664	$ 18,947	$ 57,837	$ 62,066
Weighted average common shares outstanding	56,798	58,994	57,486	59,675
Dilutive shares from assumed conversion of convertible senior notes	0	1,701	676	1,713
Dilutive stock options and restricted stock	944	1,540	1,056	1,527
Diluted weighted average common shares outstanding	57,742	62,235	59,218	62,915
Diluted net income per share	$ 0.08	$ 0.30	$ 0.98	$ 0.99