Supplemental Cash Flow Information (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Supplemental Cash Flow Information
Income taxes paid, net of refunds	$ 54,442	$ 63,899	$ 57,728
Interest paid	9,378	6,181	3,389
Assets acquired through capital leases	$ 4,491	$ 4,212	$ 2,810