Allowance for Loan Losses - Risk Category of Loans by Class of Loans (Details) - USD ($) $ in Thousands	Sep. 30, 2018	Dec. 31, 2017
Accounts Notes And Loans Receivable [Line Items]
Total loans	$ 4,440,888	$ 3,655,262
Residential Properties
Accounts Notes And Loans Receivable [Line Items]
Total loans	3,086,158	2,581,245
Commercial Real Estate
Accounts Notes And Loans Receivable [Line Items]
Total loans	841,923	696,748
Commercial and Industrial Loans
Accounts Notes And Loans Receivable [Line Items]
Total loans	410,870	310,779
Consumer Loans
Accounts Notes And Loans Receivable [Line Items]
Total loans	23,471	29,330
Land
Accounts Notes And Loans Receivable [Line Items]
Total loans	78,466	37,160
Pass
Accounts Notes And Loans Receivable [Line Items]
Total loans	4,393,856	3,623,281
Pass | Residential Properties
Accounts Notes And Loans Receivable [Line Items]
Total loans	3,079,406	2,578,773
Pass | Commercial Real Estate
Accounts Notes And Loans Receivable [Line Items]
Total loans	820,094	680,449
Pass | Commercial and Industrial Loans
Accounts Notes And Loans Receivable [Line Items]
Total loans	393,235	298,408
Pass | Consumer Loans
Accounts Notes And Loans Receivable [Line Items]
Total loans	23,471	29,330
Pass | Land
Accounts Notes And Loans Receivable [Line Items]
Total loans	77,650	36,321
Special Mention
Accounts Notes And Loans Receivable [Line Items]
Total loans	21,659	7,383
Special Mention | Residential Properties
Accounts Notes And Loans Receivable [Line Items]
Total loans	3,694	192
Special Mention | Commercial Real Estate
Accounts Notes And Loans Receivable [Line Items]
Total loans	11,086	6,326
Special Mention | Commercial and Industrial Loans
Accounts Notes And Loans Receivable [Line Items]
Total loans	6,879	865
Substandard
Accounts Notes And Loans Receivable [Line Items]
Total loans	12,838	11,162
Substandard | Residential Properties
Accounts Notes And Loans Receivable [Line Items]
Total loans	2,383	2,280
Substandard | Commercial Real Estate
Accounts Notes And Loans Receivable [Line Items]
Total loans	7,819	5,936
Substandard | Commercial and Industrial Loans
Accounts Notes And Loans Receivable [Line Items]
Total loans	1,820	2,107
Substandard | Land
Accounts Notes And Loans Receivable [Line Items]
Total loans	816	839
Impaired
Accounts Notes And Loans Receivable [Line Items]
Total loans	12,535	13,436
Impaired | Residential Properties
Accounts Notes And Loans Receivable [Line Items]
Total loans	675
Impaired | Commercial Real Estate
Accounts Notes And Loans Receivable [Line Items]
Total loans	2,924	4,037
Impaired | Commercial and Industrial Loans
Accounts Notes And Loans Receivable [Line Items]
Total loans	$ 8,936	$ 9,399