Consolidated Balance Sheets (Parenthetical) - USD ($) shares in Thousands, $ in Thousands	Mar. 31, 2019	Dec. 31, 2018
Condensed Consolidated Balance Sheets [Abstract]
Allowance for doubtful accounts, accounts receivable	$ 69	$ 1,733
Accumulated Depreciation Depletion And Amortization Property Plant And Equipment	$ 459,222	$ 460,708
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	39,169	41,357
Common stock, outstanding	39,169	41,357