Selected Quarterly Financial Data (Unaudited) (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2020	Sep. 30, 2020	Jun. 30, 2020	Mar. 31, 2020	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Quarterly Financial Information Disclosure [Abstract]
Total revenues	$ 44,137	$ 45,687	$ 44,168	$ 44,340	$ 44,228	$ 33,314	$ 46,201	$ 39,658	$ 178,332	$ 163,401	$ 156,941
Net income (loss)	$ 21,055	$ 21,552	$ 18,935	$ 19,325	$ 20,662	$ (10,054)	$ 19,698	$ 16,053	$ 80,867	$ 46,359	$ 57,923
Earnings per common share, basic (usd per share)	$ 0.22	$ 0.23	$ 0.20	$ 0.20	$ 0.22	$ (0.11)	$ 0.21	$ 0.18	$ 0.85	$ 0.49	$ 0.73
Earnings per common share, diluted (usd per share)	$ 0.22	$ 0.23	$ 0.20	$ 0.20	$ 0.22	$ (0.11)	$ 0.21	$ 0.18	$ 0.85	$ 0.49	$ 0.72
Weighted-average number of common shares outstanding, basic (shares)	95,215	95,214	95,208	95,161	95,103	95,103	94,036	88,010	95,200	93,088	79,386
Weighted-average number of common shares outstanding, diluted (shares)	95,244	95,214	95,208	95,161	95,144	95,103	94,036	88,010	95,207	93,098	79,392