CONSOLIDATED STATEMENTS OF COMPREHENSIVE INCOME - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Statement of Comprehensive Income [Abstract]
Net income	$ 181,900	$ 120,027	$ 512,351	$ 328,447
Other comprehensive (loss) income, net of tax:
Change in unrealized investment gains and losses	(12,077)	11,544	(86,452)	49,414
Benefit plan adjustments	440	(147)	1,322	(442)
Foreign currency translation adjustment	0	0	0	31
Other comprehensive (loss) income, net of tax	(11,637)	11,397	(85,130)	49,003
Comprehensive income	$ 170,263	$ 131,424	$ 427,221	$ 377,450