Loans Receivable, Net - Components of Loans Receivable, Net (Detail) - USD ($) $ in Thousands	Mar. 31, 2018	Dec. 31, 2017	Mar. 31, 2017	Dec. 31, 2016
Financing Receivable, Allowance for Credit Losses [Line Items]
Total loans	$ 5,410,493	$ 3,974,402
Purchased credit impaired ("PCI") loans	14,352	1,712
Total Loans	5,424,845	3,976,114
Deferred origination costs, net	5,752	5,380
Allowance for loan losses	(16,817)	(15,721)	$ (16,151)	$ (15,183)
Total loans, net	5,413,780	3,965,773
Commercial
Financing Receivable, Allowance for Credit Losses [Line Items]
Total loans	3,158,032	1,943,444
Commercial | Commercial And Industrial
Financing Receivable, Allowance for Credit Losses [Line Items]
Total loans	369,840	187,645
Commercial | Commercial Real Estate - Owner Occupied
Financing Receivable, Allowance for Credit Losses [Line Items]
Total loans	762,641	569,497
Commercial | Commercial Real Estate - Investor
Financing Receivable, Allowance for Credit Losses [Line Items]
Total loans	2,025,551	1,186,302
Consumer
Financing Receivable, Allowance for Credit Losses [Line Items]
Total loans	2,252,461	2,030,958
Allowance for loan losses	(507)	(614)	$ (1,136)	$ (1,110)
Consumer | Residential Mortgage
Financing Receivable, Allowance for Credit Losses [Line Items]
Total loans	1,880,287	1,748,590
Consumer | Home Equity Loans and Lines
Financing Receivable, Allowance for Credit Losses [Line Items]
Total loans	371,340	281,143
Consumer | Other Consumer
Financing Receivable, Allowance for Credit Losses [Line Items]
Total loans	$ 834	$ 1,225