Net Earnings (Loss) Per Share - Computation of Basic and Diluted Earnings Per Share (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2018	Dec. 31, 2017
Numerator (both basic and diluted):
Net loss available to common stockholders									$ (144,597)	$ (96,674)
Denominator:
Denominator for basic earnings per share (in shares)	26,570,000	26,510,000	26,444,000	26,336,000	26,049,000	26,001,000	26,011,000	25,999,000	26,467,417	26,005,870
Denominator for diluted earnings per share (in shares)	26,570,000	26,510,000	26,444,000	26,336,000	26,049,000	26,001,000	26,011,000	25,999,000	26,467,417	26,005,870
Basic loss per common share (in dollars per share)	$ (1.76)	$ (1.03)	$ (1.51)	$ (1.16)	$ (0.78)	$ (0.53)	$ (0.92)	$ (1.49)	$ (5.46)	$ (3.72)
Diluted loss per common share (in dollars per share)	$ (1.76)	$ (1.03)	$ (1.51)	$ (1.16)	$ (0.78)	$ (0.53)	$ (0.92)	$ (1.49)	$ (5.46)	$ (3.72)