Fair Value Measurements - Unobservable Input Reconciliation (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Total realized/unrealized gains (losses) [Abstract]
State premium tax credit investments, average maturity	3 years
Annual average discount rate (in hundredths)	7.10%
Total Investments [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Balance at beginning of period	$ 4,083	$ 2,167	$ 2,744
Total realized/unrealized gains (losses) [Abstract]
Included in earnings and reported as net realized investment gains	3,579
Included in earnings and reported as losses incurred, net	0	0	0
Purchases	4,258	2,541	30
Sales	(6,961)	(625)	(607)
Balance at end of period	4,959	4,083	2,167
Obligations of U.S. states and political subdivisions
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Balance at beginning of period	1,228	1,846	2,423
Total realized/unrealized gains (losses) [Abstract]
Included in earnings and reported as net realized investment gains	0
Included in earnings and reported as losses incurred, net	0	0	0
Purchases	0	7	30
Sales	(537)	(625)	(607)
Balance at end of period	691	1,228	1,846
Equity securities
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Balance at beginning of period	2,855	321	321
Total realized/unrealized gains (losses) [Abstract]
Included in earnings and reported as net realized investment gains	3,579
Included in earnings and reported as losses incurred, net	0	0	0
Purchases	4,258	2,534	0
Sales	(6,424)	0	0
Balance at end of period	4,268	2,855	321
Real Estate Acquired
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Balance at beginning of period	12,149	12,658	13,280
Total realized/unrealized gains (losses) [Abstract]
Included in earnings and reported as net realized investment gains	0
Included in earnings and reported as losses incurred, net	(1,142)	(2,322)	(4,129)
Purchases	36,859	34,624	42,247
Sales	(36,118)	(32,811)	(38,740)
Balance at end of period	$ 11,748	$ 12,149	$ 12,658