Summary of Significant Accounting Policies - Additional Information (Details) - USD ($) $ in Thousands		Jan. 01, 2019	Sep. 30, 2019	Dec. 31, 2018
Summary Of Significant Accounting Policies [Line Items]
Investment securities available-for-sale			$ 262,143	$ 328,507
Operating lease liabilities			38,116
Operating lease right-of-use assets			$ 34,965
Callable [Member]
Summary Of Significant Accounting Policies [Line Items]
Investment securities available-for-sale				11,300
Accounting Standards Update 2017-08
Summary Of Significant Accounting Policies [Line Items]
Cumulative effect of new accounting principle in period of adoption	[1]			(39)
Accounting Standards Update 2017-08 | Debt Securities [Member]
Summary Of Significant Accounting Policies [Line Items]
Reduction of unamortized premium balance		$ 49
Reduction of retained earnings, net of tax, for incremental amortization		39
Accounting Standards Update 2016-02
Summary Of Significant Accounting Policies [Line Items]
Operating lease liabilities		39,600
Operating lease right-of-use assets		36,600
Deferred rent liability		1,000
Cumulative effect of new accounting principle in period of adoption	[1]			(1,525)
Retained Earnings [Member] | Accounting Standards Update 2017-08
Summary Of Significant Accounting Policies [Line Items]
Cumulative effect of new accounting principle in period of adoption	[1]			(39)
Retained Earnings [Member] | Accounting Standards Update 2016-02
Summary Of Significant Accounting Policies [Line Items]
Cumulative effect of new accounting principle in period of adoption		1,500		$ (1,525)	[1]
Cash Flow Hedging [Member]
Summary Of Significant Accounting Policies [Line Items]
Gain on fair value hedge ineffectiveness		$ 83

[1] (1) See Note 1, "Summary of Significant Accounting Policies - Accounting Pronouncements Adopted in 2019" for additional information.