Earnings Per Share Attributable to Stockholders (Computation of Basic and Diluted 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, 2014	Sep. 30, 2014	Jun. 30, 2014	Mar. 31, 2014	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Earnings Per Share Attributable to Stockholders [Abstract]
Basic, Net income attributable to stockholders													$ 91,832	$ 136,214	$ 90,981
Diluted, Net income attributable to stockholders													$ 91,832	$ 136,214	$ 90,981
Basic, WA number of shares													106,630,323	107,075,845	107,268,425
Effect of dilutive securities: PSUs, WA number of shares													91,997
Effect of dilutive securities: Stock options, WA number of shares													735,474	356,629	386,403
Diluted, WA number of shares													107,457,794	107,432,474	107,654,828
Basic, Per share amount	$ 0.26	$ (0.05)	$ 0.37	$ 0.28	$ 0.43	$ 0.19	$ 0.42	$ 0.22	$ 0.29	$ 0.09	$ 0.35	$ 0.12	$ 0.86	$ 1.27	$ 0.85
Effect of dilutive securities: Stock options, Per share amount													(0.01)
Diluted, Per share amount	$ 0.26	$ (0.05)	$ 0.37	$ 0.27	$ 0.43	$ 0.19	$ 0.42	$ 0.22	$ 0.29	$ 0.09	$ 0.34	$ 0.12	$ 0.85	$ 1.27	$ 0.85