Earnings Per Share Attributable to Stockholders (Computation of Basic and Diluted Earnings Per Share) (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Earnings Per Share Attributable to Stockholders [Abstract]
Basic, Net income attributable to stockholders	$ 17,138	$ 10,377
Effect of dilutive securities: PSUs, Net income attributable to stockholders		27
Diluted, Net income attributable to stockholders	$ 17,138	$ 10,404
Basic, WA number of shares	107,355,381	106,851,595
Effect of dilutive securities: PSUs, WA number of shares	358,087	263,557
Effect of dilutive securities: Stock options, WA number of shares	930,429	673,797
Diluted, WA number of shares	108,643,897	107,788,949
Basic, Per share amount	$ 0.16	$ 0.10
Diluted, Per share amount	$ 0.16	$ 0.10