Supplemental Cash Flow Information (Details) - USD ($) $ in Thousands	9 Months Ended
	Sep. 30, 2015	Sep. 30, 2014
Cash paid during the period for:
Income taxes, net	$ 15,592	$ 12,608
Interest, net	1,234	637
Non-Cash Transaction Information:
Employee stock purchase plan	435	550
Equipment acquired under capital leases	553	130
Unsettled repurchases of common stock	1,011	1,937
Shares tendered in payment of the exercise price of stock options	$ 0	$ 84