Statutory Information and Restrictions - Narrative (Details) $ in Thousands	12 Months Ended
	Dec. 31, 2017 USD ($) agreement	Dec. 31, 2016 USD ($)
Insurance [Abstract]
Minimum statutory-basis capital and surplus	$ 101,463	$ 95,095
Restricted net assets of HMEC's insurance subsidiaries	17,985	18,119
Aggregate amount of dividends	94,000
Statutory capital and surplus of insurance subsidiaries	944,139	$ 912,336
Liquid assets of parent company	$ 6,464
Number of financial reinsurance agreements | agreement	0