Supplemental Cash Flow Information (Details) - USD ($) $ in Thousands	9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017
Cash Paid During the Period For:
Income taxes	$ 8,583	$ 15,204
Interest, net	3,132	2,714
Non-Cash Financing and Investing Transactions:
Employee stock purchase plan	405	399
Equipment acquired under capital leases	424	465
Shares tendered in payment of exercise price of stock options	46	0
Receivable for sale of Global's assets	0	$ 1,979
Proceeds from income tax refunds	$ 6,800