Deferred Policy Acquisition Costs - Balance RollForward (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Deferred Policy Acquisition Costs Disclosures [Abstract]
DAC balance, beginning of period	$ 1,713,065	$ 1,500,259	$ 1,351,180
Capitalization	433,575	387,396	339,639
Amortization	(209,399)	(180,582)	(157,727)
Foreign exchange translation and other	14,651	5,992	(32,833)
DAC balance, end of period	$ 1,951,892	$ 1,713,065	$ 1,500,259