CONSOLIDATED STATEMENTS OF COMPREHENSIVE INCOME - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Statement of Comprehensive Income [Abstract]
Net income	$ 143,637	$ 89,798
Other comprehensive (loss) income, net of tax:
Change in unrealized investment gains and losses	(64,453)	12,121
Benefit plan adjustments	494	(153)
Foreign currency translation adjustment	0	31
Other comprehensive (loss) income, net of tax	(63,959)	11,999
Comprehensive income	$ 79,678	$ 101,797