Loans Receivable, Net - Aging of Recorded Investment in Past Due Loans Excluding PCI Loans (Detail) - USD ($) $ in Thousands	Mar. 31, 2018	Dec. 31, 2017
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	$ 49,696	$ 36,909
Greater than 90 Days Past Due	9,670	15,471
Loans Not Past Due	5,360,797	3,937,493
Total loans	5,410,493	3,974,402
30-59 Days Past Due
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	35,911	17,315
60-89 Days Past Due
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	4,115	4,123
Residential Real Estate
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	16,771	18,920
Greater than 90 Days Past Due	1,863	3,372
Loans Not Past Due	1,863,516	1,729,670
Total loans	1,880,287	1,748,590
Residential Real Estate | 30-59 Days Past Due
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	11,766	13,197
Residential Real Estate | 60-89 Days Past Due
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	3,142	2,351
Commercial Real Estate - Owner Occupied
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	17,926	5,624
Greater than 90 Days Past Due	292	5,402
Loans Not Past Due	744,715	563,873
Total loans	762,641	569,497
Commercial Real Estate - Owner Occupied | 30-59 Days Past Due
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	17,634	222
Commercial Real Estate - Owner Occupied | 60-89 Days Past Due
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	0	0
Commercial Real Estate - Investor
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	9,258	6,068
Greater than 90 Days Past Due	4,352	4,507
Loans Not Past Due	2,016,293	1,180,234
Total loans	2,025,551	1,186,302
Commercial Real Estate - Investor | 30-59 Days Past Due
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	4,503	135
Commercial Real Estate - Investor | 60-89 Days Past Due
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	403	1,426
Consumer
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	4,042	3,064
Greater than 90 Days Past Due	1,678	1,687
Loans Not Past Due	368,132	279,304
Total loans	372,174	282,368
Consumer | 30-59 Days Past Due
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	1,794	1,067
Consumer | 60-89 Days Past Due
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	570	310
Commercial and Industrial
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	1,699	3,233
Greater than 90 Days Past Due	1,485	503
Loans Not Past Due	368,141	184,412
Total loans	369,840	187,645
Commercial and Industrial | 30-59 Days Past Due
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	214	2,694
Commercial and Industrial | 60-89 Days Past Due
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	$ 0	$ 36