Equity Securities at Fair Value - Narrative (Details) - USD ($)	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Debt and Equity Securities, FV-NI [Line Items]
Equity securities, at fair value	$ 2,710,000	$ 5,418,000
Stockholders' equity	1,079,081,000	1,011,287,000	$ 982,517,000	$ 972,060,000
Change in fair value of equity securities	(1,792,000)	767,000	305,000
Proceeds from sales of equity securities	1,390,000	0	1,065,000
Gross realized gain in equity securities	383,000		236,000
Gross realized losses in equity securities	0		0
Cumulative Effect, Period of Adoption, Adjustment
Debt and Equity Securities, FV-NI [Line Items]
Stockholders' equity				0
Cumulative Effect, Period of Adoption, Adjustment | Accounting Standards Update 2016-01
Debt and Equity Securities, FV-NI [Line Items]
Equity securities, at fair value				1,900,000
Retained Earnings
Debt and Equity Securities, FV-NI [Line Items]
Stockholders' equity	765,133,000	673,084,000	615,481,000	560,216,000
Retained Earnings | Cumulative Effect, Period of Adoption, Adjustment
Debt and Equity Securities, FV-NI [Line Items]
Stockholders' equity				548,000
Retained Earnings | Cumulative Effect, Period of Adoption, Adjustment | Accounting Standards Update 2016-01
Debt and Equity Securities, FV-NI [Line Items]
Stockholders' equity				548,000
Accumulated Other Comprehensive (Loss)
Debt and Equity Securities, FV-NI [Line Items]
Stockholders' equity	$ (45,919,000)	$ (69,625,000)	$ (68,735,000)	(71,897,000)
Accumulated Other Comprehensive (Loss) | Cumulative Effect, Period of Adoption, Adjustment
Debt and Equity Securities, FV-NI [Line Items]
Stockholders' equity				(548,000)
Accumulated Other Comprehensive (Loss) | Cumulative Effect, Period of Adoption, Adjustment | Accounting Standards Update 2016-01
Debt and Equity Securities, FV-NI [Line Items]
Stockholders' equity				$ (548,000)