Summary of Significant Accounting Policies - Additional Information (Detail) $ in Thousands	12 Months Ended
	Dec. 31, 2015 USD ($) segment entity subsidiary	Mar. 04, 2015 USD ($)	Dec. 31, 2014 USD ($)
Summary Of Significant Accounting Policies [Line Items]
Number of subsidiary | subsidiary	3
Percentage of outstanding common stock of investees accounted for using equity method of accounting	100.00%
Number of entities non-banking activities | entity	5
Assets	$ 6,318,354		$ 4,964,686
Period for satisfactory payment of TDRs	6 months
Evaluation for impairment of substandard and nonaccrual commercial loans	$ 500
Number of reporting units | segment	3
Goodwill	$ 291,764		175,820
Amortization period of intangible assets	10 years
Percentage of amount recognized of tax benefit	50.00%
Community Banking
Summary Of Significant Accounting Policies [Line Items]
Assets	$ 6,305,046		4,954,728
Goodwill	$ 287,600
Percentage of goodwill to reporting units	99.00%
Insurance
Summary Of Significant Accounting Policies [Line Items]
Assets	$ 9,619		$ 7,468
Goodwill	$ 4,200
Percentage of goodwill to reporting units	1.00%
Interest Rate Lock Commitments
Summary Of Significant Accounting Policies [Line Items]
Period for interest rate lock commitment	60 days
Integrity Bancshares, Inc.
Summary Of Significant Accounting Policies [Line Items]
Goodwill	$ 115,944	$ 115,900
Common Wealth Trust Life Insurance Company
Summary Of Significant Accounting Policies [Line Items]
Percentage of outstanding common stock of investees accounted for using equity method of accounting	50.00%
Minimum
Summary Of Significant Accounting Policies [Line Items]
Percentage of outstanding common stock of investees accounted for using equity method of accounting	20.00%
Maximum
Summary Of Significant Accounting Policies [Line Items]
Percentage of outstanding common stock of investees accounted for using equity method of accounting	50.00%
Core Deposits And Customers Lists | Minimum
Summary Of Significant Accounting Policies [Line Items]
Acquired finite-lived intangibles, weighted average life	10 years
Core Deposits And Customers Lists | Maximum
Summary Of Significant Accounting Policies [Line Items]
Acquired finite-lived intangibles, weighted average life	20 years
Corporate Joint Venture [Member]
Summary Of Significant Accounting Policies [Line Items]
Percentage of outstanding common stock of investees accounted for using equity method of accounting	50.00%