Allowance for Loan Losses - Summary of Commercial Non-ASC 310-30 and New Loans by Key Indicators of Credit Quality (Detail) - USD ($) $ in Thousands	Jun. 30, 2016	Dec. 31, 2015
Financing Receivable, Recorded Investment [Line Items]
Loans	$ 5,997,147	$ 5,193,187
New Loans
Financing Receivable, Recorded Investment [Line Items]
Loans	5,523,071	4,610,763
Acquired Loans
Financing Receivable, Recorded Investment [Line Items]
Loans	474,076	582,424
Pass | New Loans
Financing Receivable, Recorded Investment [Line Items]
Loans	3,551,546	3,033,166
Pass | Acquired Loans
Financing Receivable, Recorded Investment [Line Items]
Loans	69,077	82,235
Special Mention | New Loans
Financing Receivable, Recorded Investment [Line Items]
Loans	177	0
Special Mention | Acquired Loans
Financing Receivable, Recorded Investment [Line Items]
Loans	0	1,352
Substandard | New Loans
Financing Receivable, Recorded Investment [Line Items]
Loans	0	0
Substandard | Acquired Loans
Financing Receivable, Recorded Investment [Line Items]
Loans	8,998	9,149
Doubtful | New Loans
Financing Receivable, Recorded Investment [Line Items]
Loans	0	0
Doubtful | Acquired Loans
Financing Receivable, Recorded Investment [Line Items]
Loans	0	0
Commercial real estate
Financing Receivable, Recorded Investment [Line Items]
Loans	1,437,270	1,301,754
Commercial real estate | New Loans
Financing Receivable, Recorded Investment [Line Items]
Loans	1,209,762	998,141
Commercial real estate | Pass | New Loans
Financing Receivable, Recorded Investment [Line Items]
Loans	1,209,762	998,141
Commercial real estate | Pass | Acquired Loans
Financing Receivable, Recorded Investment [Line Items]
Loans	39,141	50,328
Commercial real estate | Special Mention | New Loans
Financing Receivable, Recorded Investment [Line Items]
Loans	0	0
Commercial real estate | Special Mention | Acquired Loans
Financing Receivable, Recorded Investment [Line Items]
Loans	0	0
Commercial real estate | Substandard | New Loans
Financing Receivable, Recorded Investment [Line Items]
Loans	0	0
Commercial real estate | Substandard | Acquired Loans
Financing Receivable, Recorded Investment [Line Items]
Loans	5,539	5,657
Commercial real estate | Doubtful | New Loans
Financing Receivable, Recorded Investment [Line Items]
Loans	0	0
Commercial real estate | Doubtful | Acquired Loans
Financing Receivable, Recorded Investment [Line Items]
Loans	0	0
Owner-occupied commercial real estate
Financing Receivable, Recorded Investment [Line Items]
Loans	590,814	545,829
Owner-occupied commercial real estate | New Loans
Financing Receivable, Recorded Investment [Line Items]
Loans	571,558	524,728
Owner-occupied commercial real estate | Pass | New Loans
Financing Receivable, Recorded Investment [Line Items]
Loans	571,381	524,728
Owner-occupied commercial real estate | Pass | Acquired Loans
Financing Receivable, Recorded Investment [Line Items]
Loans	17,036	18,854
Owner-occupied commercial real estate | Special Mention | New Loans
Financing Receivable, Recorded Investment [Line Items]
Loans	177	0
Owner-occupied commercial real estate | Special Mention | Acquired Loans
Financing Receivable, Recorded Investment [Line Items]
Loans	0	0
Owner-occupied commercial real estate | Substandard | New Loans
Financing Receivable, Recorded Investment [Line Items]
Loans	0	0
Owner-occupied commercial real estate | Substandard | Acquired Loans
Financing Receivable, Recorded Investment [Line Items]
Loans	2,220	2,247
Owner-occupied commercial real estate | Doubtful | New Loans
Financing Receivable, Recorded Investment [Line Items]
Loans	0	0
Owner-occupied commercial real estate | Doubtful | Acquired Loans
Financing Receivable, Recorded Investment [Line Items]
Loans	0	0
Construction, land and development
Financing Receivable, Recorded Investment [Line Items]
Loans	614,249	571,849
Construction, land and development | New Loans
Financing Receivable, Recorded Investment [Line Items]
Loans	582,615	537,494
Construction, land and development | Pass | New Loans
Financing Receivable, Recorded Investment [Line Items]
Loans	582,615	537,494
Construction, land and development | Pass | Acquired Loans
Financing Receivable, Recorded Investment [Line Items]
Loans	6,338	6,338
Construction, land and development | Special Mention | New Loans
Financing Receivable, Recorded Investment [Line Items]
Loans	0	0
Construction, land and development | Special Mention | Acquired Loans
Financing Receivable, Recorded Investment [Line Items]
Loans	0	0
Construction, land and development | Substandard | New Loans
Financing Receivable, Recorded Investment [Line Items]
Loans	0	0
Construction, land and development | Substandard | Acquired Loans
Financing Receivable, Recorded Investment [Line Items]
Loans	0	0
Construction, land and development | Doubtful | New Loans
Financing Receivable, Recorded Investment [Line Items]
Loans	0	0
Construction, land and development | Doubtful | Acquired Loans
Financing Receivable, Recorded Investment [Line Items]
Loans	0	0
Commercial and industrial
Financing Receivable, Recorded Investment [Line Items]
Loans	1,224,573	1,018,898
Commercial and industrial | New Loans
Financing Receivable, Recorded Investment [Line Items]
Loans	1,187,788	972,803
Commercial and industrial | Pass | New Loans
Financing Receivable, Recorded Investment [Line Items]
Loans	1,187,788	972,803
Commercial and industrial | Pass | Acquired Loans
Financing Receivable, Recorded Investment [Line Items]
Loans	6,562	6,715
Commercial and industrial | Special Mention | New Loans
Financing Receivable, Recorded Investment [Line Items]
Loans	0	0
Commercial and industrial | Special Mention | Acquired Loans
Financing Receivable, Recorded Investment [Line Items]
Loans	0	1,352
Commercial and industrial | Substandard | New Loans
Financing Receivable, Recorded Investment [Line Items]
Loans	0	0
Commercial and industrial | Substandard | Acquired Loans
Financing Receivable, Recorded Investment [Line Items]
Loans	1,239	1,245
Commercial and industrial | Doubtful | New Loans
Financing Receivable, Recorded Investment [Line Items]
Loans	0	0
Commercial and industrial | Doubtful | Acquired Loans
Financing Receivable, Recorded Investment [Line Items]
Loans	$ 0	$ 0