CONSOLIDATED STATEMENTS OF COMPREHENSIVE INCOME - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2017	Jun. 30, 2016	Jun. 30, 2017	Jun. 30, 2016
Statement of Comprehensive Income [Abstract]
Net income	$ 118,622	$ 109,221	$ 208,420	$ 178,412
Other comprehensive (loss) income, net of tax:
Change in unrealized investment gains and losses	25,749	56,338	37,870	107,165
Benefit plan adjustments	(142)	(173)	(295)	(481)
Foreign currency translation adjustment	0	11	31	(964)
Other comprehensive income, net of tax	25,607	56,176	37,606	105,720
Comprehensive income	$ 144,229	$ 165,397	$ 246,026	$ 284,132