STATEMENTS OF COMPREHENSIVE INCOME STATEMENTS OF COMPREHENSIVE INCOME - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2017	Jun. 30, 2016	Jun. 30, 2017	Jun. 30, 2016
Net income	$ 20,623	$ 20,300	$ 97,079	$ 85,044
Other comprehensive income (loss), net of tax
Change in pension and postemployment benefit plan liability, net of tax of $(81), $(73), $(161), and $(145), respectively respectively	129	115	258	231
Other comprehensive income (loss), net of tax	129	115	258	231
Comprehensive income	$ 20,752	$ 20,415	$ 97,337	$ 85,275