Income Taxes - Components of Income Tax Expense (Benefit) (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, 2017	Dec. 31, 2016	Dec. 31, 2015
Federal:
Current									$ 1,062	$ 642	$ 91
Deferred									24	387	1,090
Federal income tax provision (benefit)									1,086	1,029	1,181
State and local:
Current									402	237	122
Deferred									(1,670)	(754)	(722)
State and local income tax provision (benefit)									(1,268)	(517)	(600)
Changes in valuation allowance									1,606	493	734
Provision (benefit) for income taxes	$ 2,081	$ (1,643)	$ 641	$ 345	$ 159	$ 239	$ 117	$ 490	$ 1,424	$ 1,005	$ 1,315