CONSOLIDATED STATEMENTS OF COMPREHENSIVE INCOME - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Net Income	$ 164,172	$ 151,209	$ 120,686
Other comprehensive income (loss), net of tax:
Reclassification of net gains on derivative instruments	(1,338)	(698)	(684)
Realized loss on cash flow hedging derivatives	0	0	(11,145)
Postretirement medical liability adjustment	195	310	82
Foreign currency translation adjustment	25	558	265
Total Other Comprehensive (Loss) Income	(1,118)	170	(11,482)
Comprehensive Income	$ 163,054	$ 151,379	$ 109,204