Loans Receivable, Net - Aging of Recorded Investment in Past Due Loans Excluding PCI Loans (Detail) - USD ($) $ in Thousands	Sep. 30, 2018	Dec. 31, 2017
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	$ 42,337	$ 36,909
Greater than 90 Days Past Due	13,850	15,471
Loans Not Past Due	5,500,036	3,937,493
Total loans	5,542,373	3,974,402
30-59 Days Past Due
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	19,670	17,315
60-89 Days Past Due
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	8,817	4,123
Commercial Real Estate - Owner Occupied
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	4,506	5,624
Greater than 90 Days Past Due	197	5,402
Loans Not Past Due	730,214	563,873
Total loans	734,720	569,497
Commercial Real Estate - Owner Occupied | 30-59 Days Past Due
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	3,433	222
Commercial Real Estate - Owner Occupied | 60-89 Days Past Due
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	876	0
Commercial Real Estate - Investor
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	11,392	6,068
Greater than 90 Days Past Due	7,938	4,507
Loans Not Past Due	2,000,505	1,180,234
Total loans	2,011,897	1,186,302
Commercial Real Estate - Investor | 30-59 Days Past Due
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	2,788	135
Commercial Real Estate - Investor | 60-89 Days Past Due
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	666	1,426
Consumer
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	4,616	3,064
Greater than 90 Days Past Due	2,120	1,687
Loans Not Past Due	428,667	279,304
Total loans	433,283	282,368
Consumer | 30-59 Days Past Due
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	1,720	1,067
Consumer | 60-89 Days Past Due
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	776	310
Residential Real Estate
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	21,703	18,920
Greater than 90 Days Past Due	3,567	3,372
Loans Not Past Due	1,998,215	1,729,670
Total loans	2,019,918	1,748,590
Residential Real Estate | 30-59 Days Past Due
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	11,674	13,197
Residential Real Estate | 60-89 Days Past Due
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	6,462	2,351
Commercial and Industrial
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	120	3,233
Greater than 90 Days Past Due	28	503
Loans Not Past Due	342,435	184,412
Total loans	342,555	187,645
Commercial and Industrial | 30-59 Days Past Due
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	55	2,694
Commercial and Industrial | 60-89 Days Past Due
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	$ 37	$ 36