Investments - Net Effect on Stockholders' Equity of Unrealized Gains and Losses on Available-for-sale Securities (Details) - USD ($) $ in Thousands	Sep. 30, 2016	Dec. 31, 2015
Other Comprehensive Income (Loss), Available-for-sale Securities Adjustment, Net of Tax [Abstract]
Net unrealized investment gains including OTTI, Fixed-maturity and Equity securities	$ 110,400	$ 49,286
OTTI	103	109
Net unrealized investment gains excluding OTTI	110,503	49,395
Less deferred income taxes	(38,676)	(17,288)
Net unrealized investment gains excluding OTTI, net of tax	$ 71,827	$ 32,107