Fair Value Measurements - Unobservable Input Reconciliation (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Total Investments
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Balance at beginning of period	$ 4,539	$ 4,959	$ 4,083
Transfers out of Level 3	(3,100)
Total realized/unrealized gains (losses) [Abstract]
Included in earnings and reported as net realized investment gains	3,663		3,579
Included in earnings and reported as losses incurred, net	0	0	0
Purchases	0	0	4,258
Sales	(5,089)	(420)	(6,961)
Balance at end of period	13	4,539	4,959
Total fixed income securities
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Balance at beginning of period	271	691	1,228
Transfers out of Level 3	0
Total realized/unrealized gains (losses) [Abstract]
Included in earnings and reported as net realized investment gains	0		0
Included in earnings and reported as losses incurred, net	0	0	0
Purchases	0	0	0
Sales	(258)	(420)	(537)
Balance at end of period	13	271	691
Equity securities
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Balance at beginning of period	4,268	4,268	2,855
Transfers out of Level 3	(3,100)
Total realized/unrealized gains (losses) [Abstract]
Included in earnings and reported as net realized investment gains	3,663		3,579
Included in earnings and reported as losses incurred, net	0	0	0
Purchases	0	0	4,258
Sales	(4,831)	0	(6,424)
Balance at end of period	0	4,268	4,268
Real Estate Acquired
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Balance at beginning of period	12,713	11,748	12,149
Transfers out of Level 3	0
Total realized/unrealized gains (losses) [Abstract]
Included in earnings and reported as net realized investment gains	0		0
Included in earnings and reported as losses incurred, net	(1,995)	(1,315)	(1,142)
Purchases	33,912	34,749	36,859
Sales	(30,095)	(32,469)	(36,118)
Balance at end of period	$ 14,535	$ 12,713	$ 11,748