Supplemental Cash Flow Information (Details) - USD ($) $ in Thousands	6 Months Ended
	Jun. 30, 2016	Jun. 30, 2015
Cash paid during the period for:
Income taxes, net	$ 9,077	$ 7,971
Interest, net	1,059	807
Non-cash transaction information:
Employee stock purchase plan	384	316
Equipment acquired under capital leases	863	398
Acquisition of fixed assets through accounts payable	$ 19	$ 369