CONSOLIDATED STATEMENTS OF COMPREHENSIVE INCOME (Parenthetical) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Other comprehensive income (loss)
Amortization of losses included in net periodic benefit cost, tax	$ 2	$ 0	$ 0
Derivative instruments:
Net fair value (decrease) increase, tax	0	(20)	(43)
Reclassification of losses (gains) to net income, tax	648	39	(287)
Other Comprehensive Income (Loss), Pension and Other Postretirement Benefit Plans, Net Unamortized Gain (Loss) Arising During Period, Tax	$ (138)	$ 0	$ 0