CONSOLIDATED BALANCE SHEETS (Parenthetical) - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017
Statement of Financial Position [Abstract]
Accounts receivable, allowance for doubtful accounts (in dollars)	$ 12,827	$ 15,943
Preferred shares, authorized	5,000,000	5,000,000
Preferred shares, issued	0	0
Preferred shares, outstanding	0	0
Common shares, authorized	240,000,000	240,000,000
Common shares, issued	98,581,434	98,581,434
Common shares, outstanding	63,545,878	65,662,546
Treasury shares	35,035,556	32,918,888