Allowance for Loan Losses - Summary of Loans Based on Method for Determining Allowance (Detail) - USD ($) $ in Thousands | Jun. 30, 2018 | Mar. 31, 2018 | Dec. 31, 2017 | Jun. 30, 2017 | Mar. 31, 2017 | Dec. 31, 2016 |
Financing Receivable, Recorded Investment, Past Due [Line Items] | | | | | | |
Loans - Recorded investment, ASC 310-30 loans | $ 8,921,573 | | $ 7,977,784 | | | |
Allowance for loan losses | 50,570 | $ 49,213 | 47,145 | $ 41,334 | $ 39,431 | $ 37,897 |
New Loans | | | | | | |
Financing Receivable, Recorded Investment, Past Due [Line Items] | | | | | | |
Loans - Recorded investment, ASC 310-30 loans | 8,219,145 | | 7,661,385 | | | |
Allowance for loan losses | 47,830 | | | 37,619 | | |
Acquired Loans | | | | | | |
Financing Receivable, Recorded Investment, Past Due [Line Items] | | | | | | |
Loans - Recorded investment, ASC 310-30 loans | 702,428 | | 316,399 | | | |
Allowance for loan losses | 1,106 | | | 1,499 | | |
Unallocated Loans | | | | | | |
Financing Receivable, Recorded Investment, Past Due [Line Items] | | | | | | |
Loans - Recorded investment, Individually evaluated for impairment | 0 | | | | | |
Loans - Recorded investment, Collectively evaluated for impairment | 8,921,573 | | 7,977,784 | | | |
Allowance for credit loss, Individually evaluated for impairment | 0 | | | | | |
Allowance for credit loss, Collectively evaluated for impairment | 0 | | 1,500 | | | |
Allowance for loan losses | 0 | | | | | |
Total real estate loans | | | | | | |
Financing Receivable, Recorded Investment, Past Due [Line Items] | | | | | | |
Loans - Recorded investment, ASC 310-30 loans | 7,095,133 | | 6,318,053 | | | |
Total real estate loans | New Loans | | | | | | |
Financing Receivable, Recorded Investment, Past Due [Line Items] | | | | | | |
Loans - Recorded investment, Individually evaluated for impairment | 2,231 | | 1,226 | | | |
Loans - Recorded investment, Collectively evaluated for impairment | 6,475,280 | | 6,019,803 | | | |
Loans - Recorded investment, ASC 310-30 loans | 6,477,511 | | 6,021,029 | | | |
Allowance for credit loss, Individually evaluated for impairment | 66 | | 66 | | | |
Allowance for credit loss, Collectively evaluated for impairment | 29,210 | | 27,736 | | | |
Total real estate loans | Acquired Loans | | | | | | |
Financing Receivable, Recorded Investment, Past Due [Line Items] | | | | | | |
Loans - Recorded investment, Individually evaluated for impairment | 4,551 | | 4,655 | | | |
Loans - Recorded investment, Collectively evaluated for impairment | 412,088 | | 147,354 | | | |
Allowance for credit loss, Individually evaluated for impairment | 117 | | 129 | | | |
Allowance for credit loss, Collectively evaluated for impairment | 668 | | 683 | | | |
Commercial real estate | | | | | | |
Financing Receivable, Recorded Investment, Past Due [Line Items] | | | | | | |
Loans - Recorded investment, ASC 310-30 loans | 2,605,589 | | 2,245,859 | | | |
Allowance for loan losses | 15,381 | 14,197 | 13,870 | 12,155 | 9,964 | 10,123 |
Commercial real estate | New Loans | | | | | | |
Financing Receivable, Recorded Investment, Past Due [Line Items] | | | | | | |
Loans - Recorded investment, Individually evaluated for impairment | 465 | | 0 | | | |
Loans - Recorded investment, Collectively evaluated for impairment | 2,361,010 | | 2,103,788 | | | |
Loans - Recorded investment, ASC 310-30 loans | 2,361,475 | | 2,103,788 | | | |
Allowance for credit loss, Individually evaluated for impairment | 0 | | 0 | | | |
Allowance for credit loss, Collectively evaluated for impairment | 13,850 | | 12,084 | | | |
Allowance for loan losses | 13,850 | | | 10,146 | | |
Commercial real estate | Acquired Loans | | | | | | |
Financing Receivable, Recorded Investment, Past Due [Line Items] | | | | | | |
Loans - Recorded investment, Individually evaluated for impairment | 3,789 | | 3,893 | | | |
Loans - Recorded investment, Collectively evaluated for impairment | 102,734 | | 33,843 | | | |
Allowance for credit loss, Individually evaluated for impairment | 117 | | 129 | | | |
Allowance for credit loss, Collectively evaluated for impairment | 197 | | 209 | | | |
Allowance for loan losses | 314 | | | 331 | | |
Commercial real estate | Unallocated Loans | | | | | | |
Financing Receivable, Recorded Investment, Past Due [Line Items] | | | | | | |
Allowance for loan losses | 0 | | | | | |
Owner-occupied commercial real estate | | | | | | |
Financing Receivable, Recorded Investment, Past Due [Line Items] | | | | | | |
Loans - Recorded investment, ASC 310-30 loans | 1,199,019 | | 1,003,881 | | | |
Allowance for loan losses | 3,946 | 3,778 | 3,365 | 3,286 | 2,711 | 2,597 |
Owner-occupied commercial real estate | New Loans | | | | | | |
Financing Receivable, Recorded Investment, Past Due [Line Items] | | | | | | |
Loans - Recorded investment, Individually evaluated for impairment | 0 | | 0 | | | |
Loans - Recorded investment, Collectively evaluated for impairment | 1,119,816 | | 987,781 | | | |
Loans - Recorded investment, ASC 310-30 loans | 1,119,816 | | 987,781 | | | |
Allowance for credit loss, Individually evaluated for impairment | 0 | | 0 | | | |
Allowance for credit loss, Collectively evaluated for impairment | 3,892 | | 3,310 | | | |
Allowance for loan losses | 3,892 | | | 3,221 | | |
Owner-occupied commercial real estate | Acquired Loans | | | | | | |
Financing Receivable, Recorded Investment, Past Due [Line Items] | | | | | | |
Loans - Recorded investment, Individually evaluated for impairment | 0 | | 0 | | | |
Loans - Recorded investment, Collectively evaluated for impairment | 79,203 | | 16,100 | | | |
Allowance for credit loss, Individually evaluated for impairment | 0 | | 0 | | | |
Allowance for credit loss, Collectively evaluated for impairment | 54 | | 55 | | | |
Allowance for loan losses | 54 | | | 65 | | |
Owner-occupied commercial real estate | Unallocated Loans | | | | | | |
Financing Receivable, Recorded Investment, Past Due [Line Items] | | | | | | |
Allowance for loan losses | 0 | | | | | |
1-4 single family residential | | | | | | |
Financing Receivable, Recorded Investment, Past Due [Line Items] | | | | | | |
Loans - Recorded investment, ASC 310-30 loans | 2,416,159 | | 2,270,570 | | | |
Allowance for loan losses | 7,310 | 7,493 | 7,978 | 8,749 | 7,913 | 7,379 |
1-4 single family residential | New Loans | | | | | | |
Financing Receivable, Recorded Investment, Past Due [Line Items] | | | | | | |
Loans - Recorded investment, Individually evaluated for impairment | 1,637 | | 1,096 | | | |
Loans - Recorded investment, Collectively evaluated for impairment | 2,225,198 | | 2,184,266 | | | |
Loans - Recorded investment, ASC 310-30 loans | 2,226,835 | | 2,185,362 | | | |
Allowance for credit loss, Individually evaluated for impairment | 0 | | 0 | | | |
Allowance for credit loss, Collectively evaluated for impairment | 7,139 | | 7,769 | | | |
Allowance for loan losses | 7,139 | | | 8,482 | | |
1-4 single family residential | Acquired Loans | | | | | | |
Financing Receivable, Recorded Investment, Past Due [Line Items] | | | | | | |
Loans - Recorded investment, Individually evaluated for impairment | 267 | | 267 | | | |
Loans - Recorded investment, Collectively evaluated for impairment | 155,525 | | 57,428 | | | |
Allowance for credit loss, Individually evaluated for impairment | 0 | | 0 | | | |
Allowance for credit loss, Collectively evaluated for impairment | 156 | | 184 | | | |
Allowance for loan losses | 156 | | | 242 | | |
1-4 single family residential | Unallocated Loans | | | | | | |
Financing Receivable, Recorded Investment, Past Due [Line Items] | | | | | | |
Allowance for loan losses | 0 | | | | | |
Construction, land and development | | | | | | |
Financing Receivable, Recorded Investment, Past Due [Line Items] | | | | | | |
Loans - Recorded investment, ASC 310-30 loans | 771,478 | | 703,518 | | | |
Allowance for loan losses | 4,076 | 4,288 | 4,345 | 4,713 | 4,918 | 4,677 |
Construction, land and development | New Loans | | | | | | |
Financing Receivable, Recorded Investment, Past Due [Line Items] | | | | | | |
Loans - Recorded investment, Individually evaluated for impairment | 0 | | 0 | | | |
Loans - Recorded investment, Collectively evaluated for impairment | 708,497 | | 684,462 | | | |
Loans - Recorded investment, ASC 310-30 loans | 708,497 | | 684,462 | | | |
Allowance for credit loss, Individually evaluated for impairment | 0 | | 0 | | | |
Allowance for credit loss, Collectively evaluated for impairment | 3,893 | | 4,164 | | | |
Allowance for loan losses | 3,893 | | | 4,490 | | |
Construction, land and development | Acquired Loans | | | | | | |
Financing Receivable, Recorded Investment, Past Due [Line Items] | | | | | | |
Loans - Recorded investment, Individually evaluated for impairment | 0 | | 0 | | | |
Loans - Recorded investment, Collectively evaluated for impairment | 33,121 | | 5,889 | | | |
Allowance for credit loss, Individually evaluated for impairment | 0 | | 0 | | | |
Allowance for credit loss, Collectively evaluated for impairment | 59 | | 36 | | | |
Allowance for loan losses | 59 | | | 38 | | |
Construction, land and development | Unallocated Loans | | | | | | |
Financing Receivable, Recorded Investment, Past Due [Line Items] | | | | | | |
Allowance for loan losses | 0 | | | | | |
Home equity loans and lines of credit | | | | | | |
Financing Receivable, Recorded Investment, Past Due [Line Items] | | | | | | |
Loans - Recorded investment, ASC 310-30 loans | 102,888 | | 94,225 | | | |
Allowance for loan losses | 704 | 616 | 674 | 884 | 726 | 648 |
Home equity loans and lines of credit | New Loans | | | | | | |
Financing Receivable, Recorded Investment, Past Due [Line Items] | | | | | | |
Loans - Recorded investment, Individually evaluated for impairment | 129 | | 130 | | | |
Loans - Recorded investment, Collectively evaluated for impairment | 60,759 | | 59,506 | | | |
Loans - Recorded investment, ASC 310-30 loans | 60,888 | | 59,636 | | | |
Allowance for credit loss, Individually evaluated for impairment | 66 | | 66 | | | |
Allowance for credit loss, Collectively evaluated for impairment | 436 | | 409 | | | |
Allowance for loan losses | 502 | | | 433 | | |
Home equity loans and lines of credit | Acquired Loans | | | | | | |
Financing Receivable, Recorded Investment, Past Due [Line Items] | | | | | | |
Loans - Recorded investment, Individually evaluated for impairment | 495 | | 495 | | | |
Loans - Recorded investment, Collectively evaluated for impairment | 41,505 | | 34,094 | | | |
Allowance for credit loss, Individually evaluated for impairment | 0 | | 0 | | | |
Allowance for credit loss, Collectively evaluated for impairment | 202 | | 199 | | | |
Allowance for loan losses | 202 | | | 451 | | |
Home equity loans and lines of credit | Unallocated Loans | | | | | | |
Financing Receivable, Recorded Investment, Past Due [Line Items] | | | | | | |
Allowance for loan losses | 0 | | | | | |
Total other loans | | | | | | |
Financing Receivable, Recorded Investment, Past Due [Line Items] | | | | | | |
Loans - Recorded investment, ASC 310-30 loans | 1,826,440 | | 1,659,731 | | | |
Total other loans | New Loans | | | | | | |
Financing Receivable, Recorded Investment, Past Due [Line Items] | | | | | | |
Loans - Recorded investment, Individually evaluated for impairment | 16,708 | | 0 | | | |
Loans - Recorded investment, Collectively evaluated for impairment | 1,724,926 | | 1,640,356 | | | |
Loans - Recorded investment, ASC 310-30 loans | 1,741,634 | | 1,640,356 | | | |
Allowance for credit loss, Individually evaluated for impairment | 1,594 | | 0 | | | |
Allowance for credit loss, Collectively evaluated for impairment | 16,960 | | 14,823 | | | |
Total other loans | Acquired Loans | | | | | | |
Financing Receivable, Recorded Investment, Past Due [Line Items] | | | | | | |
Loans - Recorded investment, Individually evaluated for impairment | 3,420 | | 272 | | | |
Loans - Recorded investment, Collectively evaluated for impairment | 60,125 | | 5,049 | | | |
Allowance for credit loss, Individually evaluated for impairment | 272 | | 272 | | | |
Allowance for credit loss, Collectively evaluated for impairment | 49 | | 47 | | | |
Commercial and industrial | | | | | | |
Financing Receivable, Recorded Investment, Past Due [Line Items] | | | | | | |
Loans - Recorded investment, ASC 310-30 loans | 1,804,764 | | 1,652,065 | | | |
Allowance for loan losses | 18,934 | 17,114 | 15,141 | 11,296 | 12,953 | 12,245 |
Commercial and industrial | New Loans | | | | | | |
Financing Receivable, Recorded Investment, Past Due [Line Items] | | | | | | |
Loans - Recorded investment, Individually evaluated for impairment | 16,708 | | 0 | | | |
Loans - Recorded investment, Collectively evaluated for impairment | 1,720,777 | | 1,634,372 | | | |
Loans - Recorded investment, ASC 310-30 loans | 1,737,485 | | 1,634,372 | | | |
Allowance for credit loss, Individually evaluated for impairment | 1,594 | | 0 | | | |
Allowance for credit loss, Collectively evaluated for impairment | 16,883 | | 14,702 | | | |
Allowance for loan losses | 18,477 | | | 10,762 | | |
Commercial and industrial | Acquired Loans | | | | | | |
Financing Receivable, Recorded Investment, Past Due [Line Items] | | | | | | |
Loans - Recorded investment, Individually evaluated for impairment | 3,420 | | 272 | | | |
Loans - Recorded investment, Collectively evaluated for impairment | 43,887 | | 4,790 | | | |
Allowance for credit loss, Individually evaluated for impairment | 272 | | 272 | | | |
Allowance for credit loss, Collectively evaluated for impairment | 46 | | 41 | | | |
Allowance for loan losses | 318 | | | 366 | | |
Commercial and industrial | Unallocated Loans | | | | | | |
Financing Receivable, Recorded Investment, Past Due [Line Items] | | | | | | |
Allowance for loan losses | 0 | | | | | |
Consumer | | | | | | |
Financing Receivable, Recorded Investment, Past Due [Line Items] | | | | | | |
Loans - Recorded investment, ASC 310-30 loans | 21,676 | | 7,666 | | | |
Allowance for loan losses | 219 | $ 227 | 272 | 251 | $ 246 | $ 228 |
Consumer | New Loans | | | | | | |
Financing Receivable, Recorded Investment, Past Due [Line Items] | | | | | | |
Loans - Recorded investment, Individually evaluated for impairment | 0 | | 0 | | | |
Loans - Recorded investment, Collectively evaluated for impairment | 4,149 | | 5,984 | | | |
Loans - Recorded investment, ASC 310-30 loans | 4,149 | | 5,984 | | | |
Allowance for credit loss, Individually evaluated for impairment | 0 | | 0 | | | |
Allowance for credit loss, Collectively evaluated for impairment | 77 | | 121 | | | |
Allowance for loan losses | 77 | | | 85 | | |
Consumer | Acquired Loans | | | | | | |
Financing Receivable, Recorded Investment, Past Due [Line Items] | | | | | | |
Loans - Recorded investment, Individually evaluated for impairment | 0 | | 0 | | | |
Loans - Recorded investment, Collectively evaluated for impairment | 16,238 | | 259 | | | |
Allowance for credit loss, Individually evaluated for impairment | 0 | | 0 | | | |
Allowance for credit loss, Collectively evaluated for impairment | 3 | | 6 | | | |
Allowance for loan losses | 3 | | | 6 | | |
Consumer | Unallocated Loans | | | | | | |
Financing Receivable, Recorded Investment, Past Due [Line Items] | | | | | | |
Allowance for loan losses | 0 | | | | | |
ASC 310-30 Loans | Acquired Loans | | | | | | |
Financing Receivable, Recorded Investment, Past Due [Line Items] | | | | | | |
Loans - Recorded investment, ASC 310-30 loans | 222,244 | | 159,069 | | | |
Allowance for loan losses | 1,634 | | | 2,216 | | |
ASC 310-30 Loans | Unallocated Loans | | | | | | |
Financing Receivable, Recorded Investment, Past Due [Line Items] | | | | | | |
Loans - Recorded investment, ASC 310-30 loans | 0 | | | | | |
Allowance for loan losses | 0 | | | | | |
ASC 310-30 Loans | Total real estate loans | New Loans | | | | | | |
Financing Receivable, Recorded Investment, Past Due [Line Items] | | | | | | |
Loans - Recorded investment, ASC 310-30 loans | 0 | | 0 | | | |
Allowance for loan losses | 0 | | 0 | | | |
ASC 310-30 Loans | Total real estate loans | Acquired Loans | | | | | | |
Financing Receivable, Recorded Investment, Past Due [Line Items] | | | | | | |
Loans - Recorded investment, ASC 310-30 loans | 200,983 | | 145,015 | | | |
Allowance for loan losses | 1,356 | | 1,618 | | | |
ASC 310-30 Loans | Commercial real estate | New Loans | | | | | | |
Financing Receivable, Recorded Investment, Past Due [Line Items] | | | | | | |
Loans - Recorded investment, ASC 310-30 loans | 0 | | 0 | | | |
Allowance for loan losses | 0 | | 0 | | | |
ASC 310-30 Loans | Commercial real estate | Acquired Loans | | | | | | |
Financing Receivable, Recorded Investment, Past Due [Line Items] | | | | | | |
Loans - Recorded investment, ASC 310-30 loans | 137,591 | | 104,335 | | | |
Allowance for loan losses | 1,217 | | 1,448 | 1,678 | | |
ASC 310-30 Loans | Owner-occupied commercial real estate | New Loans | | | | | | |
Financing Receivable, Recorded Investment, Past Due [Line Items] | | | | | | |
Loans - Recorded investment, ASC 310-30 loans | 0 | | 0 | | | |
Allowance for loan losses | 0 | | 0 | | | |
ASC 310-30 Loans | Owner-occupied commercial real estate | Acquired Loans | | | | | | |
Financing Receivable, Recorded Investment, Past Due [Line Items] | | | | | | |
Loans - Recorded investment, ASC 310-30 loans | 0 | | 0 | | | |
Allowance for loan losses | 0 | | 0 | 0 | | |
ASC 310-30 Loans | 1-4 single family residential | New Loans | | | | | | |
Financing Receivable, Recorded Investment, Past Due [Line Items] | | | | | | |
Loans - Recorded investment, ASC 310-30 loans | 0 | | 0 | | | |
Allowance for loan losses | 0 | | 0 | | | |
ASC 310-30 Loans | 1-4 single family residential | Acquired Loans | | | | | | |
Financing Receivable, Recorded Investment, Past Due [Line Items] | | | | | | |
Loans - Recorded investment, ASC 310-30 loans | 33,532 | | 27,513 | | | |
Allowance for loan losses | 15 | | 25 | 25 | | |
ASC 310-30 Loans | Construction, land and development | New Loans | | | | | | |
Financing Receivable, Recorded Investment, Past Due [Line Items] | | | | | | |
Loans - Recorded investment, ASC 310-30 loans | 0 | | 0 | | | |
Allowance for loan losses | 0 | | 0 | | | |
ASC 310-30 Loans | Construction, land and development | Acquired Loans | | | | | | |
Financing Receivable, Recorded Investment, Past Due [Line Items] | | | | | | |
Loans - Recorded investment, ASC 310-30 loans | 29,860 | | 13,167 | | | |
Allowance for loan losses | 124 | | 145 | 185 | | |
ASC 310-30 Loans | Home equity loans and lines of credit | New Loans | | | | | | |
Financing Receivable, Recorded Investment, Past Due [Line Items] | | | | | | |
Loans - Recorded investment, ASC 310-30 loans | 0 | | 0 | | | |
Allowance for loan losses | 0 | | 0 | | | |
ASC 310-30 Loans | Home equity loans and lines of credit | Acquired Loans | | | | | | |
Financing Receivable, Recorded Investment, Past Due [Line Items] | | | | | | |
Loans - Recorded investment, ASC 310-30 loans | 0 | | 0 | | | |
Allowance for loan losses | 0 | | 0 | 0 | | |
ASC 310-30 Loans | Total other loans | New Loans | | | | | | |
Financing Receivable, Recorded Investment, Past Due [Line Items] | | | | | | |
Loans - Recorded investment, ASC 310-30 loans | 0 | | 0 | | | |
Allowance for loan losses | 0 | | 0 | | | |
ASC 310-30 Loans | Total other loans | Acquired Loans | | | | | | |
Financing Receivable, Recorded Investment, Past Due [Line Items] | | | | | | |
Loans - Recorded investment, ASC 310-30 loans | 21,261 | | 14,054 | | | |
Allowance for loan losses | 278 | | 271 | | | |
ASC 310-30 Loans | Commercial and industrial | New Loans | | | | | | |
Financing Receivable, Recorded Investment, Past Due [Line Items] | | | | | | |
Loans - Recorded investment, ASC 310-30 loans | 0 | | 0 | | | |
Allowance for loan losses | 0 | | 0 | | | |
ASC 310-30 Loans | Commercial and industrial | Acquired Loans | | | | | | |
Financing Receivable, Recorded Investment, Past Due [Line Items] | | | | | | |
Loans - Recorded investment, ASC 310-30 loans | 19,972 | | 12,631 | | | |
Allowance for loan losses | 139 | | 126 | 168 | | |
ASC 310-30 Loans | Consumer | New Loans | | | | | | |
Financing Receivable, Recorded Investment, Past Due [Line Items] | | | | | | |
Loans - Recorded investment, ASC 310-30 loans | 0 | | 0 | | | |
Allowance for loan losses | 0 | | 0 | | | |
ASC 310-30 Loans | Consumer | Acquired Loans | | | | | | |
Financing Receivable, Recorded Investment, Past Due [Line Items] | | | | | | |
Loans - Recorded investment, ASC 310-30 loans | 1,289 | | 1,423 | | | |
Allowance for loan losses | $ 139 | | $ 145 | $ 160 | | |