EARNINGS PER SHARE - Components of Basic and Diluted EPS (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, 2018	Dec. 31, 2017	Dec. 31, 2016
Earnings Per Share [Abstract]
Net Income Attributable to Common Shareholders	$ 231,300	$ 289,400	$ 242,800	$ 269,500	$ 237,400	$ 260,400	$ 230,700	$ 259,500	$ 1,033,000	$ 987,996	$ 942,302
Weighted Average Common Shares Outstanding:
Basic (in shares)									317,370,369	317,411,097	317,650,180
Dilutive Effect (in shares)									623,565	620,483	804,059
Diluted (in shares)									317,993,934	318,031,580	318,454,239
Basic EPS (in dollars per share)									$ 3.25	$ 3.11	$ 2.97
Diluted EPS (in dollars per share)									$ 3.25	$ 3.11	$ 2.96