STATEMENTS OF COMPREHENSIVE INCOME - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Statement of Comprehensive Income [Abstract]
Net income	$ 288,224	$ 196,999	$ 210,366
Other comprehensive income (loss), net of tax
Change in unrealized holding (losses) gains on available-for-sale securities	(9,937)	(190)	43
Pension and other postretirement plans	35,712	(8,105)	(24,560)
OCI (loss)	25,775	(8,295)	(24,517)
Comprehensive income	$ 313,999	$ 188,704	$ 185,849