Securities - Additional Information (Detail) (USD $) In Thousands, unless otherwise specified	3 Months Ended		6 Months Ended
	Jun. 30, 2013 Securities	Jun. 30, 2012	Jun. 30, 2013 Securities	Jun. 30, 2012	Dec. 31, 2012
Schedule of Available-for-sale Securities [Line Items]
Number of securities holdings	0		0
Shareholders' equity percentage	10.00%		10.00%
Amortized Cost	$ 727,426		$ 727,426		$ 712,637
Fair Value	724,298		724,298		737,311
Number of structured pooled trust preferred securities deemed to be other-than-temporarily impaired	4		4		4
Securities	311,493		311,493		264,813
Pooled Trust Preferred [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	800		800		800
Fair Value	630		630		600
Four Structured Pool Trust Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Number of Pooled Trust Securities	1		1
Amortized Cost	0		0		0
Other than temporary impairment recognized in earnings for available for sale securities	$ 0	$ 0	$ 0	$ 0