Computation of Basic and Diluted Net Income Per Share (Detail) (USD $) In Thousands, except Share data, unless otherwise specified	3 Months Ended		6 Months Ended
	Jun. 30, 2013	Jun. 30, 2012	Jun. 30, 2013	Jun. 30, 2012
Basic net income per share:
Net income applicable to common stockholders	$ 14,135	$ 1,942	$ 19,870	$ 7,006
Undistributed earnings allocated to participating securities	(112)	(16)	(169)	(60)
Net income applicable to common stockholders excluding amounts applicable to participating securities	14,023	1,926	19,701	6,946
Weighted average common shares outstanding	68,442	68,323	68,419	68,284
Basic net income per share	$ 0.20	$ 0.03	$ 0.29	$ 0.10
Diluted net income per share:
Net income applicable to common stockholders	14,135	1,942	19,870	7,006
Undistributed earnings allocated to participating securities	(112)	(16)	(169)	(60)
Net income applicable to common stockholders excluding amounts applicable to participating securities	$ 14,023	$ 1,926	$ 19,701	$ 6,946
Weighted average common shares outstanding	68,442	68,323	68,419	68,284
Dilutive stock options and restricted stock	416	202	425	287
Diluted weighted average common shares outstanding	68,858	68,525	68,844	68,571
Diluted net income per share	$ 0.20	$ 0.25	$ 0.29	$ 0.44