Earnings Per Share (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Numerator:
Net income (loss) attributable to common shareholders	$ 14,334	$ (43,897)	$ 69,949	$ 6,566	$ 16,428	$ 31,631	$ 20,004	$ 655	$ 46,952	$ 68,718	$ 47,787
Less: dividends paid on unvested share-based compensation									(483)	(432)	(459)
Net income (loss) available to common shareholders									$ 46,469	$ 68,286	$ 47,328
Denominator:
Weighted-average number of common shares-basic									71,901,499	71,715,870	65,646,712
Effect of dilutive share-based compensation									471,743	668,419	617,406
Weighted-average number of common shares-diluted									72,373,242	72,384,289	66,264,118
Net income (loss) per share available to common shareholders, basic (in usd per share)	$ 0.20	$ (0.61)	$ 0.97	$ 0.09	$ 0.23	$ 0.44	$ 0.28	$ 0.01	$ 0.65	$ 0.95	$ 0.72
Net income (loss) per share available to common shareholders, diluted (in usd per share)	$ 0.20	$ (0.61)	$ 0.96	$ 0.09	$ 0.23	$ 0.43	$ 0.27	$ 0.01	$ 0.64	$ 0.94	$ 0.71
Antidilutive securities excluded from computation of earnings per share, amount (in shares)									114,889	0	0