Allowance for Loan Losses - Bank's Allowance for Loan Losses (Details) - USD ($) $ in Thousands	3 Months Ended												12 Months Ended
	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Financing Receivable Allowance For Credit Losses [Line Items]
Beginning Balance				$ 15,400				$ 10,600				$ 10,150	$ 15,400	$ 10,600	$ 10,150
Provision for loan losses	$ 900	$ 701	$ 1,092	69	$ 1,800	$ 1,231	$ 1,250	400	$ 1,200	$ 570	$ 753	150	2,762	4,681	2,673
Charge-offs														(50)	(2,223)
Recoveries													238	169
Ending Balance	18,400				15,400				10,600				18,400	15,400	10,600
Residential Properties
Financing Receivable Allowance For Credit Losses [Line Items]
Beginning Balance				6,669				6,799				6,546	6,669	6,799	6,546
Provision for loan losses													3,046	(130)	253
Ending Balance	9,715				6,669				6,799				9,715	6,669	6,799
Commercial Real Estate
Financing Receivable Allowance For Credit Losses [Line Items]
Beginning Balance				2,983				1,813				1,499	2,983	1,813	1,499
Provision for loan losses													1,416	1,051	624
Charge-offs														(50)	(310)
Recoveries														169
Ending Balance	4,399				2,983				1,813				4,399	2,983	1,813
Land and Construction
Financing Receivable Allowance For Credit Losses [Line Items]
Beginning Balance				233				103				67	233	103	67
Provision for loan losses													162	130	36
Ending Balance	395				233				103				395	233	103
Commercial and Industrial Loans
Financing Receivable Allowance For Credit Losses [Line Items]
Beginning Balance				5,227				1,649				1,897	5,227	1,649	1,897
Provision for loan losses													(1,841)	3,578	1,665
Charge-offs															(1,913)
Recoveries													238
Ending Balance	3,624				5,227				1,649				3,624	5,227	1,649
Consumer Loans
Financing Receivable Allowance For Credit Losses [Line Items]
Beginning Balance				$ 288				$ 236				$ 141	288	236	141
Provision for loan losses													(21)	52	95
Ending Balance	$ 267				$ 288				$ 236				$ 267	$ 288	$ 236