Schedule II - Valuation and Qualifying Accounts (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Allowance for Doubtful Accounts [Member]
Movement in Valuation Allowances and Reserves [Roll Forward]
Balance at Beginning of Period	$ 8,857	$ 6,212	$ 10,826
Charged to Costs & Expenses	9,633	8,508	1,736
Charged to Other Accounts	0	0	0
Deductions	(10,261)	(5,863)	(6,350)
Balance at End of Period	8,229	8,857	6,212
Claim Losses [Member]
Movement in Valuation Allowances and Reserves [Roll Forward]
Balance at Beginning of Period	26,939	25,344	24,871
Charged to Costs & Expenses	15,272	15,816	10,448
Charged to Other Accounts	0	0	0
Deductions	(15,332)	(14,221)	(9,975)
Balance at End of Period	26,879	26,939	25,344
Valuation Allowance of Deferred Tax Assets [Member]
Movement in Valuation Allowances and Reserves [Roll Forward]
Balance at Beginning of Period	44,879	19,171	21,911
Charged to Costs & Expenses	(1,072)	25,946	(2,645)
Charged to Other Accounts	1,359	(238)	(95)
Deductions	0	0	0
Balance at End of Period	$ 45,166	$ 44,879	$ 19,171