Allowance for Loan Losses - Summary of Commercial Non-ASC 310-30 and New Loans by Key Indicators of Credit Quality (Detail) - USD ($) $ in Thousands	Mar. 31, 2018	Dec. 31, 2017
Financing Receivable, Recorded Investment [Line Items]
Loans	$ 8,704,392	$ 7,977,784
New Loans
Financing Receivable, Recorded Investment [Line Items]
Loans	7,976,251	7,661,385
Acquired Loans
Financing Receivable, Recorded Investment [Line Items]
Loans	728,141	316,399
Pass | New Loans
Financing Receivable, Recorded Investment [Line Items]
Loans	5,639,551	5,385,265
Pass | Acquired Loans
Financing Receivable, Recorded Investment [Line Items]
Loans	268,495	59,316
Special Mention | New Loans
Financing Receivable, Recorded Investment [Line Items]
Loans	34,238	22,976
Special Mention | Acquired Loans
Financing Receivable, Recorded Investment [Line Items]
Loans	0	0
Substandard | New Loans
Financing Receivable, Recorded Investment [Line Items]
Loans	3,095	2,162
Substandard | Acquired Loans
Financing Receivable, Recorded Investment [Line Items]
Loans	5,506	5,471
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	2,418,753	2,245,859
Commercial real estate | New Loans
Financing Receivable, Recorded Investment [Line Items]
Loans	2,168,606	2,103,788
Commercial real estate | Pass | New Loans
Financing Receivable, Recorded Investment [Line Items]
Loans	2,159,454	2,095,560
Commercial real estate | Pass | Acquired Loans
Financing Receivable, Recorded Investment [Line Items]
Loans	107,104	33,496
Commercial real estate | Special Mention | New Loans
Financing Receivable, Recorded Investment [Line Items]
Loans	6,057	6,066
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	3,095	2,162
Commercial real estate | Substandard | Acquired Loans
Financing Receivable, Recorded Investment [Line Items]
Loans	4,190	4,240
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	1,156,610	1,003,881
Owner-occupied commercial real estate | New Loans
Financing Receivable, Recorded Investment [Line Items]
Loans	1,074,076	987,781
Owner-occupied commercial real estate | Pass | New Loans
Financing Receivable, Recorded Investment [Line Items]
Loans	1,074,076	987,781
Owner-occupied commercial real estate | Pass | Acquired Loans
Financing Receivable, Recorded Investment [Line Items]
Loans	81,953	15,607
Owner-occupied commercial real estate | Special Mention | New Loans
Financing Receivable, Recorded Investment [Line Items]
Loans	0	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	581	493
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	796,152	703,518
Construction, land and development | New Loans
Financing Receivable, Recorded Investment [Line Items]
Loans	732,551	684,462
Construction, land and development | Pass | New Loans
Financing Receivable, Recorded Investment [Line Items]
Loans	732,551	684,462
Construction, land and development | Pass | Acquired Loans
Financing Receivable, Recorded Investment [Line Items]
Loans	32,413	5,889
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	1,771,845	1,652,065
Commercial and industrial | New Loans
Financing Receivable, Recorded Investment [Line Items]
Loans	1,701,651	1,634,372
Commercial and industrial | Pass | New Loans
Financing Receivable, Recorded Investment [Line Items]
Loans	1,673,470	1,617,462
Commercial and industrial | Pass | Acquired Loans
Financing Receivable, Recorded Investment [Line Items]
Loans	47,025	4,324
Commercial and industrial | Special Mention | New Loans
Financing Receivable, Recorded Investment [Line Items]
Loans	28,181	16,910
Commercial and industrial | Special Mention | Acquired Loans
Financing Receivable, Recorded Investment [Line Items]
Loans	0	0
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	735	738
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