Earnings Per Share - Basic and Diluted Earnings Per Share (Detail) (USD $) In Thousands, except Per 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 available to common shareholders	$ 9,424	$ 7,005	$ 17,786	$ 13,239
Weighted average common shares outstanding	46,427	46,460	46,376	46,247
Basic net income per share	$ 0.20	$ 0.15	$ 0.38	$ 0.29
Dilutive net income per share:
Net income available to common shareholders	$ 9,424	$ 7,005	$ 17,786	$ 13,239
Weighted average common shares outstanding	46,427	46,460	46,376	46,247
Dilutive stock options and non-vested restricted stock	1,827	1,354	1,773	1,352
Weighted average common shares outstanding for purposes of computing diluted net income per share	48,254	47,814	48,149	47,599
Dilutive net income per share	$ 0.20	$ 0.15	$ 0.37	$ 0.28