Long-Term Borrowings and Subordinated Debt - Additional Information (Detail) - USD ($)			1 Months Ended	12 Months Ended
	Jun. 18, 2015	Mar. 05, 2015	Jun. 30, 2013	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013	Mar. 04, 2015
Debt Instrument [Line Items]
Early repayment of junior subordinated debt			$ 45,000,000	$ 13,500,000	$ 0	$ 45,000,000
Long-term borrowings				117,000,000	$ 19,300,000
Total loans pledged as collateral				2,800,000,000
Maximum eligible borrowing based on qualifying collateral				1,400,000,000.0
Maximum borrowing capacity				1,900,000,000.0
Capital lease				$ 200,000
Percentage of equity owned				100.00%
2006 Junior Subordinated Debt | Integrity Bancshares, Inc.
Debt Instrument [Line Items]
Junior Subordinated Debt Assumed on Acquisition							$ 13,500,000
Junior Subordinated Debt Paid Off	$ 5,000,000	$ 8,500,000