Summary of Significant Accounting Policies - Additional Information (Details) - USD ($) $ in Thousands		9 Months Ended
	Jan. 01, 2019	Sep. 30, 2018	Dec. 31, 2017
Summary Of Significant Accounting Policies [Line Items]
Tax Cuts and Jobs Act of 2017, Reclassification from AOCI to Retained Earnings, Tax Effect		$ 3,900
Investments in equity securities			$ 7,061
Investment securities available-for-sale		336,933	391,457
Equity Securities [Member]
Summary Of Significant Accounting Policies [Line Items]
Investments in equity securities			1,076
Equity Securities Available-for-Sale, Unrealized net gain			666
Available-for-sale Securities, Accumulated Net Gain Net of Income Taxes			433
Money Market Mutual Funds [Member]
Summary Of Significant Accounting Policies [Line Items]
Investments in equity securities			$ 5,985
Callable [Member]
Summary Of Significant Accounting Policies [Line Items]
Investment securities available-for-sale		11,300
Other Noninterest Income [Member] | Equity Securities [Member]
Summary Of Significant Accounting Policies [Line Items]
Net realized gain on investment securities		$ 26
Forecast [Member] | Accounting Standards Update 2017-08 | Debt Securities [Member]
Summary Of Significant Accounting Policies [Line Items]
Reduction of unamortized premium balance	$ 50
Reduction of retained earnings, net of tax, for incremental amortization	40
Forecast [Member] | Accounting Standards Update 2016-02 | Minimum [Member]
Summary Of Significant Accounting Policies [Line Items]
Operating lease, liability	30,000
Operating lease, right-of-use asset	30,000
Forecast [Member] | Accounting Standards Update 2016-02 | Maximum [Member]
Summary Of Significant Accounting Policies [Line Items]
Operating lease, liability	40,000
Operating lease, right-of-use asset	$ 40,000