Allowance for Loan Losses - Summary of Allowance for Loan Losses (Detail) - USD ($)	3 Months Ended								12 Months Ended
	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2014	Sep. 30, 2014	Jun. 30, 2014	Mar. 31, 2014	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013	Mar. 04, 2015
Financing Receivable, Allowance for Credit Losses [Roll Forward]
Balance at beginning of year				$ 47,911,000				$ 46,255,000	$ 47,911,000	$ 46,255,000
Charge-offs									(15,266,000)	(6,353,000)
Recoveries									5,114,000	6,294,000
Net (Charge-offs)/ Recoveries									(10,152,000)	(59,000)
Provision for loan losses	$ 3,915,000	$ 3,206,000	$ 2,059,000	1,207,000	$ 1,106,000	$ 1,454,000	$ (1,134,000)	289,000	10,388,000	1,715,000	$ 8,311,000
Balance at End of Year	48,147,000				47,911,000				48,147,000	47,911,000	46,255,000
Total Loans	5,062,933,000				3,871,716,000				5,062,933,000	3,871,716,000
Commercial Real Estate
Financing Receivable, Allowance for Credit Losses [Roll Forward]
Balance at beginning of year				20,164,000				18,921,000	20,164,000	18,921,000
Charge-offs									(2,787,000)	(2,041,000)
Recoveries									3,545,000	1,798,000
Net (Charge-offs)/ Recoveries									758,000	(243,000)
Provision for loan losses									(5,879,000)	1,486,000
Balance at End of Year	15,043,000				20,164,000				15,043,000	20,164,000	18,921,000
Total Loans	2,166,603,000				1,682,236,000				2,166,603,000	1,682,236,000
Commercial and Industrial
Financing Receivable, Allowance for Credit Losses [Roll Forward]
Balance at beginning of year				13,668,000				14,433,000	13,668,000	14,433,000
Charge-offs									(5,463,000)	(1,267,000)
Recoveries									605,000	3,647,000
Net (Charge-offs)/ Recoveries									(4,858,000)	2,380,000
Provision for loan losses									2,043,000	(3,145,000)
Balance at End of Year	10,853,000				13,668,000				10,853,000	13,668,000	14,433,000
Total Loans	1,256,830,000				994,138,000				1,256,830,000	994,138,000
Commercial Construction
Financing Receivable, Allowance for Credit Losses [Roll Forward]
Balance at beginning of year				6,093,000				5,374,000	6,093,000	5,374,000
Charge-offs									(3,321,000)	(712,000)
Recoveries									143,000	146,000
Net (Charge-offs)/ Recoveries									(3,178,000)	(566,000)
Provision for loan losses									9,710,000	1,285,000
Balance at End of Year	12,625,000				6,093,000				12,625,000	6,093,000	5,374,000
Total Loans	413,444,000				216,148,000				413,444,000	216,148,000
Consumer Real Estate
Financing Receivable, Allowance for Credit Losses [Roll Forward]
Balance at beginning of year				6,333,000				6,362,000	6,333,000	6,362,000
Charge-offs									(2,167,000)	(1,200,000)
Recoveries									495,000	350,000
Net (Charge-offs)/ Recoveries									(1,672,000)	(850,000)
Provision for loan losses									3,739,000	821,000
Balance at End of Year	8,400,000				6,333,000				8,400,000	6,333,000	6,362,000
Other Consumer
Financing Receivable, Allowance for Credit Losses [Roll Forward]
Balance at beginning of year				$ 1,653,000				$ 1,165,000	1,653,000	1,165,000
Charge-offs									(1,528,000)	(1,133,000)
Recoveries									326,000	353,000
Net (Charge-offs)/ Recoveries									(1,202,000)	(780,000)
Provision for loan losses									775,000	1,268,000
Balance at End of Year	1,226,000				$ 1,653,000				1,226,000	$ 1,653,000	$ 1,165,000
Integrity Bancshares, Inc.
Financing Receivable, Allowance for Credit Losses [Roll Forward]
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Allowance for Loan Losses	0								0			$ 0
Total Loans	673,300,000								673,300,000
Loans	788,687,000								788,687,000			788,700,000
Integrity Bancshares, Inc. | Commercial Real Estate
Financing Receivable, Allowance for Credit Losses [Roll Forward]
Total Loans	293,200,000								293,200,000
Loans												331,600,000
Integrity Bancshares, Inc. | Commercial Construction
Financing Receivable, Allowance for Credit Losses [Roll Forward]
Total Loans	$ 69,200,000								$ 69,200,000
Loans												$ 92,400,000