CONSOLIDATED STATEMENTS OF COMPREHENSIVE INCOME - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018
Statement of Comprehensive Income [Abstract]
Net income	$ 151,941	$ 143,637
Other comprehensive income (loss), net of tax:
Change in unrealized investment gains and losses	81,071	(64,453)
Benefit plan adjustments	1,650	494
Other comprehensive income (loss), net of tax	82,721	(63,959)
Comprehensive income	$ 234,662	$ 79,678