Earnings (Loss) per Share (Details) - USD ($) shares in Thousands, $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Numerator [Abstract]
Net income (loss) attributable to controlling interest	$ (40,674)	$ 14,420	$ (20,407)	$ 29,540
Denominator [Abstract]
Denominator for basic earnings (loss) per share (in shares)	23,061	23,026	23,053	23,020
Effect of dilutive securities [Abstract]
Restricted stock units (in shares)	0	93	0	97
Supplemental Executive Retirement Plan (in shares)	0	64	0	62
Denominator for diluted earnings (loss) per share (in shares)	23,061	23,183	23,053	23,179