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, 2016	Sep. 30, 2015	Sep. 30, 2016	Sep. 30, 2015
Basic net income per share:
Net income applicable to common stockholders	$ 33,378	$ 31,880	$ 96,433	$ 71,002
Weighted average common shares outstanding	63,604	66,524	64,488	67,608
Basic net income per share	$ 0.52	$ 0.48	$ 1.50	$ 1.05
Diluted net income per share:
Net income applicable to common stockholders	$ 33,378	$ 31,880	$ 96,433	$ 71,002
Weighted average common shares outstanding	63,604	66,524	64,488	67,608
Dilutive shares from assumed conversion of convertible senior notes	1,172	611	743	1,462
Dilutive stock options and restricted stock	1,256	907	1,222	1,019
Diluted weighted average common shares outstanding	66,032	68,042	66,453	70,089
Diluted net income per share	$ 0.51	$ 0.47	$ 1.45	$ 1.01