Earnings (Loss) per Share (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017	Dec. 31, 2017
Basic:
Net income (loss) attributable to controlling interests and available to common shareholders	$ 8,781	$ (175,561)	$ 9,780	$ (161,304)
Net income (loss) available to common shareholders	8,781	(175,561)	9,780	(161,304)
Diluted:
Net income (loss) available to common shareholders and assumed conversions	$ 8,781	$ (175,561)	$ 9,780	$ (161,304)
Weighted Average Shares Outstanding
Weighted Average Shares Outstanding, Basic	46,073,739	45,662,543	45,945,728	45,597,558
Stock options added to the denominator under the treasury stock method	9,894		664
RSUs added to the denominator under the treasury stock method	393,154		440,131
Weighted Average Shares Outstanding, Diluted	46,476,787	45,662,543	46,386,523	45,597,558
Net income (loss) per common share – basic	$ 0.19	$ (3.84)	$ 0.21	$ (3.54)
Net income (loss) per common share – diluted	$ 0.19	$ (3.84)	$ 0.21	$ (3.54)
Convertible Senior Notes 1.00 percent due 2020
Earnings (Loss) per Share
Face amount of debt issuance	$ 287,500		$ 287,500
Interest rate, as a percentage	1.00%		1.00%		1.00%