Allowance for Loan Losses - Risk Category of Loans by Class of Loans (Details) - USD ($) $ in Thousands	Mar. 31, 2018	Dec. 31, 2017
Accounts Notes And Loans Receivable [Line Items]
Total loans	$ 3,905,684	$ 3,655,262
Residential Properties
Accounts Notes And Loans Receivable [Line Items]
Total loans	2,799,370	2,581,245
Commercial Real Estate
Accounts Notes And Loans Receivable [Line Items]
Total loans	708,458	696,748
Commercial and Industrial Loans
Accounts Notes And Loans Receivable [Line Items]
Total loans	337,295	310,779
Consumer Loans
Accounts Notes And Loans Receivable [Line Items]
Total loans	29,361	29,330
Land
Accounts Notes And Loans Receivable [Line Items]
Total loans	31,200	37,160
Pass
Accounts Notes And Loans Receivable [Line Items]
Total loans	3,874,657	3,623,281
Pass \| Residential Properties
Accounts Notes And Loans Receivable [Line Items]
Total loans	2,796,111	2,578,773
Pass \| Commercial Real Estate
Accounts Notes And Loans Receivable [Line Items]
Total loans	693,082	680,449
Pass \| Commercial and Industrial Loans
Accounts Notes And Loans Receivable [Line Items]
Total loans	325,731	298,408
Pass \| Consumer Loans
Accounts Notes And Loans Receivable [Line Items]
Total loans	29,361	29,330
Pass \| Land
Accounts Notes And Loans Receivable [Line Items]
Total loans	30,372	36,321
Special Mention
Accounts Notes And Loans Receivable [Line Items]
Total loans	9,304	7,383
Special Mention \| Residential Properties
Accounts Notes And Loans Receivable [Line Items]
Total loans	3,259	192
Special Mention \| Commercial Real Estate
Accounts Notes And Loans Receivable [Line Items]
Total loans	5,885	6,326
Special Mention \| Commercial and Industrial Loans
Accounts Notes And Loans Receivable [Line Items]
Total loans	160	865
Substandard
Accounts Notes And Loans Receivable [Line Items]
Total loans	8,399	11,162
Substandard \| Residential Properties
Accounts Notes And Loans Receivable [Line Items]
Total loans		2,280
Substandard \| Commercial Real Estate
Accounts Notes And Loans Receivable [Line Items]
Total loans	5,509	5,936
Substandard \| Commercial and Industrial Loans
Accounts Notes And Loans Receivable [Line Items]
Total loans	2,062	2,107
Substandard \| Land
Accounts Notes And Loans Receivable [Line Items]
Total loans	828	839
Impaired
Accounts Notes And Loans Receivable [Line Items]
Total loans	13,324	13,436
Impaired \| Commercial Real Estate
Accounts Notes And Loans Receivable [Line Items]
Total loans	3,982	4,037
Impaired \| Commercial and Industrial Loans
Accounts Notes And Loans Receivable [Line Items]
Total loans	$ 9,342	$ 9,399