Consolidated Balance Sheets (Parenthetical) - USD ($) $ in Thousands	Dec. 31, 2016	Dec. 31, 2015
Statement Of Financial Position [Abstract]
Trade accounts receivable, allowance for doubtful accounts	$ 8,396	$ 8,923
Common shares, par value	$ 0.10	$ 0.10
Common shares, authorized	50,000,000	50,000,000
Common shares, issued	17,828,155	18,659,696
Common shares, outstanding	17,828,155	18,659,696