CONSOLIDATED STATEMENTS OF COMPREHENSIVE INCOME (UNAUDITED) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2017	Mar. 31, 2016
Comprehensive income:
Net income	$ 111,546	$ 115,874
Amortization of losses (gains) included in net periodic benefit cost, net of tax of $1 and $135, respectively	1	(219)
Derivative instruments:
Net fair value increase, net of tax of $0, and $(1), respectively	0	(2)
Reclassification of losses to net income, net of tax of $152 and $163, respectively	246	264
Other comprehensive income	247	43
Comprehensive income	$ 111,793	$ 115,917