CONSOLIDATED STATEMENTS OF COMPREHENSIVE INCOME - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Statement of Comprehensive Income [Abstract]
Net income	$ 186,814	$ 118,622	$ 330,451	$ 208,420
Other comprehensive (loss) income, net of tax:
Change in unrealized investment gains and losses	(9,922)	25,749	(74,375)	37,870
Benefit plan adjustments	388	(142)	882	(295)
Foreign currency translation adjustment	0	0	0	31
Other comprehensive (loss) income, net of tax	(9,534)	25,607	(73,493)	37,606
Comprehensive income	$ 177,280	$ 144,229	$ 256,958	$ 246,026