Property and Casualty Unpaid Claims and Claim Expenses - Narrative (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Insurance Loss Reserves [Abstract]
Automobile liability coverage percent reserves	80.00%
Short tail coverage reserves as a percentage of total reserves	15.00%
Long tail coverage reserves as percentage of reserves	85.00%
Percentage of losses incurred	99.00%
Potential variability of property and casualty loss reserves	6.00%
Probability of other possible outcomes possible impact on net income	$ 10,000
Favorable development of total reserves for property and casualty claims occurring in prior years	$ 2,700	$ 7,000	$ 12,500