Deferred Policy Acquisition Costs (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Movement Analysis of Deferred Policy Acquisition Costs [Roll Forward]
Balance, beginning of year	$ 200,826	$ 201,762	$ 197,202
Policy acquisition costs deferred	552,675	561,610	543,791
Amortization	(555,350)	(562,546)	(539,231)
Balance, end of year	$ 198,151	$ 200,826	$ 201,762