CONSOLIDATED STATEMENTS OF COMPREHENSIVE INCOME (LOSS) - USD ($) $ in Thousands	3 Months Ended												12 Months Ended
	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Comprehensive income (loss)
Net income	$ 125,329	$ 26,551	$ 2,261	$ 15,318	$ 19,823	$ 26,923	$ 11,866	$ 25,153	$ 21,040	$ 21,984	$ 16,183	$ 34,275	$ 169,459	$ 83,765	$ 93,482
Other comprehensive income (loss), net of taxes:
Change in net unrealized investment gains and losses on fixed maturity and equity securities													74,405	571	(122,387)
Change in net funded status of benefit plans													734	(23)	1,159
Other comprehensive income (loss)													75,139	548	(121,228)
Total													$ 244,598	$ 84,313	$ (27,746)