Fair Value of Financial Instruments - Changes in Fair Value of Level 3 Financial Assets (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2020	Mar. 31, 2019
Fair Value Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation
Balance as of	$ 15,912	$ 22,956
Total gains (losses) included in net income	(375)	(405)
Total gains (losses) included in other comprehensive income	154	131
Sales	(277)
Balance as of	15,414	22,682
Change in unrealized gains (losses) for the period included in net income for assets held at the end of the reporting period	(375)	(405)
Change in unrealized gains (losses) for the period included in other comprehensive income for assets held at the end of the reporting period	154
States and political subdivision bonds
Fair Value Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation
Balance as of	3,100	3,596
Total gains (losses) included in net income	0	0
Total gains (losses) included in other comprehensive income	0	64
Sales	0
Balance as of	3,100	3,660
Change in unrealized gains (losses) for the period included in net income for assets held at the end of the reporting period	0	0
Change in unrealized gains (losses) for the period included in other comprehensive income for assets held at the end of the reporting period	0
Corporate bonds
Fair Value Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation
Balance as of	8,328	11,767
Total gains (losses) included in net income	0	0
Total gains (losses) included in other comprehensive income	154	67
Sales	0
Balance as of	8,482	11,834
Change in unrealized gains (losses) for the period included in net income for assets held at the end of the reporting period	0	0
Change in unrealized gains (losses) for the period included in other comprehensive income for assets held at the end of the reporting period	154
Other investments
Fair Value Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation
Balance as of	4,484	7,593
Total gains (losses) included in net income	(375)	(405)
Total gains (losses) included in other comprehensive income	0	0
Sales	(277)
Balance as of	3,832	7,188
Change in unrealized gains (losses) for the period included in net income for assets held at the end of the reporting period	(375)	$ (405)
Change in unrealized gains (losses) for the period included in other comprehensive income for assets held at the end of the reporting period	$ 0