Income Taxes - Components of income tax expense (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Current
Federal expense	$ 3,905	$ 2,761	$ 1,955
State and city expense	1,206	799	387
Total current tax expense	5,111	3,560	2,342
Deferred
Federal (benefit) expense	153	(257)	444
State and city (benefit) expense	(269)	(113)	604
Total deferred tax (benefit) expense	(116)	(370)	1,048
Income tax expense	$ 4,995	$ 3,190	$ 3,390