Policy Claims and Benefits (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018	Dec. 31, 2018	Dec. 31, 2017
Liability for Unpaid Claims and Claims Adjustment Expense [Roll Forward]
Liability for Claims and Claims Adjustment Expense	$ 6,933,305	$ 6,320,426	$ 6,584,668	$ 5,896,469
Reinsurance Recoverable for Unpaid Claims and Claims Adjustments	(499,562)	(469,419)	(432,582)	(455,547)
Liability For Unpaid Claims And Claims Adjustment Expense Net Of Recoverable	6,433,743	5,851,007	$ 6,152,086	$ 5,440,922
Current Year Claims and Claims Adjustment Expense	2,807,937	2,663,116
Prior Year Claims and Claims Adjustment Expense	31,447	6,255
Liability for Unpaid Claims and Claims Adjustment Expense, Incurred Claims	2,839,384	2,669,371
Liability for Unpaid Claims and Claims Adjustment Expense, Claims Paid, Current Year	(186,601)	(180,802)
Liability for Unpaid Claims and Claims Adjustment Expense, Claims Paid, Prior Years	(2,387,312)	(2,111,275)
Liability for Unpaid Claims and Claims Adjustment Expense, Claims Paid	(2,573,913)	(2,292,077)
Interest On Liability For Policy And Contract Claims	6,556	6,115
Liability for Unpaid Claims and Claims Adjustment Expense, Foreign Currency Translation Gain (Loss)	9,630	26,676
Liability for Unpaid Claims and Claims Adjustment Expense Other	$ 16,186	$ 32,791