Fair Value Measurements - Unobservable Input Reconciliation (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Total Investments
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Balance at beginning of period	$ 1,360	$ 4,845	$ 4,539	$ 4,959
Transfers out of Level 3			(3,100)
Total realized gains (losses):
Included in earnings and reported as net realized investment gains	3,663		3,663
Included in earnings and reported as losses incurred, net	0	0	0	0
Purchases	0	0	0	0
Sales	(115)	(197)	(194)	(311)
Balance at end of period	4,908	4,648	4,908	4,648
Debt Securities
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Balance at beginning of period	192	577	271	691
Transfers out of Level 3			0
Total realized gains (losses):
Included in earnings and reported as net realized investment gains	0		0
Included in earnings and reported as losses incurred, net	0	0	0	0
Purchases	0	0	0	0
Sales	(115)	(197)	(194)	(311)
Balance at end of period	77	380	77	380
Equity securities
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Balance at beginning of period	1,168	4,268	4,268	4,268
Transfers out of Level 3			(3,100)
Total realized gains (losses):
Included in earnings and reported as net realized investment gains	3,663		3,663
Included in earnings and reported as losses incurred, net	0	0	0	0
Purchases	0	0	0	0
Sales	0	0	0	0
Balance at end of period	4,831	4,268	4,831	4,268
Real Estate Acquired
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Balance at beginning of period	13,321	10,271	12,713	11,748
Transfers out of Level 3			0
Total realized gains (losses):
Included in earnings and reported as net realized investment gains	0		0
Included in earnings and reported as losses incurred, net	(450)	(592)	(1,104)	(818)
Purchases	7,979	8,881	24,742	26,985
Sales	(8,511)	(6,832)	(24,012)	(26,187)
Balance at end of period	$ 12,339	$ 11,728	$ 12,339	$ 11,728