Loans Receivable, Net - Components of Loans Receivable, Net (Detail) - USD ($) $ in Thousands	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017
Financing Receivable, Allowance for Credit Losses [Line Items]
Total loans	$ 5,938,453		$ 5,579,812
Purchased credit impaired (“PCI”) loans	13,432		8,901
Total Loans	5,951,885		5,588,713
Deferred origination costs, net	8,180		7,086
Allowance for loan losses	(16,135)	$ (16,705)	(16,577)	$ (16,691)	$ (16,817)	$ (15,721)
Total loans, net	5,943,930		5,579,222
Commercial
Financing Receivable, Allowance for Credit Losses [Line Items]
Total loans	3,294,080		3,060,579
Commercial | Commercial and industrial
Financing Receivable, Allowance for Credit Losses [Line Items]
Total loans	391,588		304,994
Commercial | Commercial real estate – owner occupied
Financing Receivable, Allowance for Credit Losses [Line Items]
Total loans	770,730		740,375
Commercial | Commercial real estate – investor
Financing Receivable, Allowance for Credit Losses [Line Items]
Total loans	2,131,762		2,015,210
Consumer
Financing Receivable, Allowance for Credit Losses [Line Items]
Total loans	2,644,373		2,519,233
Allowance for loan losses	(512)	$ (367)	(486)	$ (526)	$ (507)	$ (614)
Consumer | Residential real estate
Financing Receivable, Allowance for Credit Losses [Line Items]
Total loans	2,193,489		2,044,286
Consumer | Home equity loans and lines
Financing Receivable, Allowance for Credit Losses [Line Items]
Total loans	341,869		353,386
Consumer | Other consumer
Financing Receivable, Allowance for Credit Losses [Line Items]
Total loans	$ 109,015		$ 121,561