Earnings (Loss) Per Share Attributable to Stockholders (Computation of Basic and Diluted Earnings Per Share) (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2016	Sep. 30, 2015	Sep. 30, 2016	Sep. 30, 2015
Earnings (Loss) Per Share Attributable to Stockholders [Abstract]
Basic, Net income attributable to stockholders	$ (5,137)	$ 20,825	$ 63,979	$ 89,685
Diluted, Net income attributable to stockholders	$ (5,137)	$ 20,825	$ 63,979	$ 89,685
Basic, WA number of shares	106,622,376	107,137,417	106,595,088	107,041,819
Effect of dilutive securities: PSUs, WA number of shares	81,610		27,203
Effect of dilutive securities: Stock options, WA number of shares	821,065	380,471	599,099	391,540
Diluted, WA number of shares	107,525,051	107,517,888	107,221,390	107,433,359
Basic, Per share amount	$ (0.05)	$ 0.19	$ 0.60	$ 0.84
Effect of dilutive securities: Stock options, Per share amount				(0.01)
Diluted, Per share amount	$ (0.05)	$ 0.19	$ 0.60	$ 0.83