Quarterly Financial Information (unaudited) (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Quarterly Financial Data [Abstract]
Total income	$ 13,716	$ 15,316	$ 20,703	$ 15,184	$ 13,894	$ 14,750	$ 14,777	$ 14,743	$ 64,919	$ 58,164	$ 54,795
Income before provision for income tax	7,107	8,250	13,664	8,192	7,269	7,579	8,215	8,338	37,213	31,401	30,285
Net income attributable to common stockholders	$ 6,657	$ 7,691	$ 13,027	$ 7,330	$ 6,596	$ 6,558	$ 7,521	$ 7,665	$ 34,705	$ 28,340	$ 28,927
Basic earnings per common share (in dollars per share)	$ 0.31	$ 0.39	$ 0.67	$ 0.39	$ 0.35	$ 0.35	$ 0.40	$ 0.41	$ 1.74	$ 1.50	$ 1.58
Diluted earnings per common share (in dollars per share)	$ 0.31	$ 0.36	$ 0.56	$ 0.36	$ 0.34	$ 0.34	$ 0.37	$ 0.38	$ 1.59	$ 1.43	$ 1.51