Loans and Loans Held for Sale - Additional Information (Detail) $ in Thousands	3 Months Ended	6 Months Ended
	Jun. 30, 2015 USD ($) SecurityLoan	Jun. 30, 2015 USD ($) SecurityLoan	Mar. 04, 2015 USD ($)	Dec. 31, 2014 USD ($)
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans and Leases Receivable, Deferred Income	$ 14,000	$ 14,000		$ 2,100
Discount on loans related to purchase accounting fair value adjustments	$ 14,700	$ 14,700
Percentage of commercial loans in total portfolio loans	76.00%	76.00%		75.00%
Commercial Loans	$ 3,639,300	$ 3,639,300		$ 2,892,522
Concentration Risk, Product		no
Maximum concentration of commercial real estate and commercial construction portfolio in loans (in excess of)	7.00%	7.00%		7.00%
Minimum period of loan payment defaults following restructure for TDRs to be in default		90 days
Commercial Real Estate and Commercial Construction [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Commercial Loans	$ 2,400,000	$ 2,400,000
Combined percentage of commercial real estate and commercial construction in total commercial loans	66.00%	66.00%		66.00%
Combined percentage of commercial real estate and commercial construction in total portfolio loans	50.00%	50.00%		49.00%
Out Of State Exposure Of Combined Portfolio	6.30%	6.30%		8.00%
Percentage of total loans out-of-state excluding contiguous states	3.10%	3.10%		3.90%
Construction Loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Commercial Loans	$ 344,983	$ 344,983		$ 216,148
Number Of Loans Modified Not Considered To Be Troubled Debt Restructuring | SecurityLoan	4	4
Loans modified not considered to be troubled debt restructuring	$ 1,300	$ 1,300
Commercial Real Estate [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Commercial Loans	$ 2,054,935	$ 2,054,935		1,682,236
Number Of Loans Modified Not Considered To Be Troubled Debt Restructuring | SecurityLoan	1	3
Loans modified not considered to be troubled debt restructuring	$ 800	$ 1,000
Home Equity [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Number Of Loans Modified Not Considered To Be Troubled Debt Restructuring | SecurityLoan	2	2
Loans modified not considered to be troubled debt restructuring	$ 200	$ 200
Commercial and Industrial [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Commercial Loans	$ 1,239,382	$ 1,239,382		$ 994,138
Number Of Loans Modified Not Considered To Be Troubled Debt Restructuring | SecurityLoan	4	6
Loans modified not considered to be troubled debt restructuring	$ 5,500	$ 5,700
Integrity Bancshares, Inc. [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Discount on loans related to purchase accounting fair value adjustments			$ 14,800
Integrity Bancshares, Inc. [Member] | Commercial Real Estate and Commercial Construction [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Commercial Loans	$ 424,000	$ 424,000