Earnings Per Common Share - Reconciliation of Earnings Per Share Calculations (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Earnings per Common Share
Net income	$ (25,837)	$ 2,755	$ 110	$ 573	$ 5,012	$ 478	$ 2,825	$ 2,199	$ (22,399)	$ 10,514	$ 42,151
Weighted average common shares outstanding:
Basic (in shares)									39,802	39,719	39,568
Incremental shares with dilutive effect:
Restricted stock awards (in shares)										63	168
Diluted (in shares)									39,802	39,782	39,736
Basic income (loss) per share:
Basic (in dollars per share)	$ (0.65)	$ 0.07	$ 0.00	$ 0.01	$ 0.13	$ 0.01	$ 0.07	$ 0.06	$ (0.56)	$ 0.27	$ 1.07
Diluted income (loss) per share:
Diluted (in dollars per share)	$ (0.65)	$ 0.07	$ 0.00	$ 0.01	$ 0.13	$ 0.01	$ 0.07	$ 0.06	$ (0.56)	$ 0.27	$ 1.06