Goodwill and Other Intangible Assets - Schedule of Changes in Carrying Amount of Goodwill (Detail) (USD $) In Thousands, unless otherwise specified	6 Months Ended
	Jun. 30, 2013	Jun. 30, 2012
Goodwill [Line Items]
Balance	$ 338,820	$ 253,177
Goodwill acquired during the period	562
Ending balance	339,382	253,177
Community Banking [Member]
Goodwill [Line Items]
Balance	297,055	212,412
Goodwill acquired during the period	562
Ending balance	297,617	212,412
Other Segment [Member]
Goodwill [Line Items]
Balance	41,765	40,765
Goodwill acquired during the period
Ending balance	$ 41,765	$ 40,765