Consolidated Balance Sheets (Parenthetical) - USD ($) shares in Thousands, $ in Thousands	Sep. 30, 2017	Dec. 31, 2016
Consolidated Balance Sheets [Abstract]
Allowance for doubtful accounts, accounts receivable	$ 1,802	$ 2,838
Accumulated Depreciation Depletion And Amortization Property Plant And Equipment	$ 423,520	$ 406,375
Preferred shares, par value	$ 0.1	$ 0.1
Preferred shares, shares authorized	5,000	5,000
Preferred shares, issued	0	0
Common stock, par value	$ 0.1	$ 0.1
Common stock, shares authorized	145,000	145,000
Common stock, issued	49,822	49,330
Common stock, outstanding	49,822	49,330