Segments - Total Assets by Reportable Operating Segment (Detail) (USD $) In Thousands, unless otherwise specified	3 Months Ended
	Mar. 31, 2015 segment	Dec. 31, 2014
Segment Reporting, Asset Reconciling Item [Line Items]
Number of Reportable Segments	3
Total Assets	$ 5,971,293	$ 4,964,686
Community Banking [Member]
Segment Reporting, Asset Reconciling Item [Line Items]
Total Assets	5,959,651	4,954,728
Insurance [Member]
Segment Reporting, Asset Reconciling Item [Line Items]
Total Assets	8,098	7,468
Wealth Management [Member]
Segment Reporting, Asset Reconciling Item [Line Items]
Total Assets	$ 3,544	$ 2,490