STATEMENTS OF COMPREHENSIVE INCOME STATEMENTS OF COMPREHENSIVE INCOME - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Net income	$ 16,276	$ 18,797	$ 127,530	$ 115,876
Other comprehensive income (loss), net of tax
Change in pension and postemployment benefit plan liability, net of tax of $(68), $(81), (419) and (161), respectively	203	128	326	386
Other comprehensive income, net of tax	203	128	326	386
Comprehensive income	$ 16,479	$ 18,925	$ 127,856	$ 116,262