Earnings Per Share (Reconciliation of the numerator and denominator of basic earnings per share with that of diluted earnings per share) (Detail) (USD $) In Thousands, except Share data, unless otherwise specified	3 Months Ended		6 Months Ended
	Jun. 30, 2012	Jun. 30, 2011	Jun. 30, 2012	Jun. 30, 2011
Basic
Net Income	$ 21,049	$ 17,452	$ 42,059	$ 35,337
Average common shares outstanding	50,274,665	43,645,541	50,255,019	43,637,497
Earnings per basic common share	$ 0.42	$ 0.40	$ 0.84	$ 0.81
Diluted
Net Income	$ 21,049	$ 17,452	$ 42,059	$ 35,337
Average common shares outstanding	50,274,665	43,645,541	50,255,019	43,637,497
Equivalents from stock options	33,563	30,866	44,963	48,706
Average diluted shares outstanding	50,308,228	43,676,407	50,299,982	43,686,203
Earnings per diluted common share	$ 0.42	$ 0.40	$ 0.84	$ 0.81