Earnings Per Share Attributable to Stockholders (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended												12 Months Ended
	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Earnings Per Share Attributable to Stockholders [Abstract]
Basic, Net income attributable to stockholders													$ 121,479	$ 75,027	$ 91,832
Effect of dilutive securities: Share units, Net income attributable to stockholders														(152)
Diluted, Net income attributable to stockholders													$ 121,479	$ 74,875	$ 91,832
Basic, WA number of shares													108,063,349	107,044,348	106,630,323
Effect of dilutive securities: Share units, WA number of shares													459,503	353,880	91,997
Effect of dilutive securities: Stock options, WA number of shares													865,384	714,923	735,474
Diluted, WA number of shares													109,388,236	108,113,151	107,457,794
Basic, Per share amount	$ 0.33	$ 0.21	$ 0.42	$ 0.16	$ 0.34	$ 0.10	$ 0.16	$ 0.10	$ 0.26	$ (0.05)	$ 0.37	$ 0.28	$ 1.12	$ 0.70	$ 0.86
Effect of dilutive securities: Stock options, Per share amount													(0.01)	(0.01)	(0.01)
Diluted, Per share amount	$ 0.32	$ 0.21	$ 0.42	$ 0.16	$ 0.34	$ 0.09	$ 0.16	$ 0.10	$ 0.26	$ (0.05)	$ 0.37	$ 0.27	$ 1.11	$ 0.69	$ 0.85