Supplemental Cash Flow Information (Details) - USD ($) $ in Thousands	9 Months Ended
	Sep. 30, 2016	Sep. 30, 2015
Cash paid during the period for:
Income taxes, net	$ 16,023	$ 15,592
Interest, net	1,569	1,234
Non-cash transaction information:
Employee stock purchase plan	528	435
Equipment acquired under capital leases	1,123	553
Unsettled repurchase of common stock	0	1,011
Acquisition of fixed assets through accounts payable	$ 19	$ 86