Earnings Per Share (Details) - USD ($) $ / shares in Units, shares in Thousands, $ 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 earnings		$ 115,041	$ 116,287	$ 115,735	$ 118,276					$ 465,339	$ 357,818	$ 352,166
Participating Securities, Distributed and Undistributed Earnings (Loss), Basic	[1]									5,119	4,184
Net earnings from continuing operations						$ 84,037	$ 101,466	$ 93,647	$ 78,668	465,339	357,818
Undistributed Earnings (Loss) Allocated to Participating Securities, Basic	[1]											(3,988)
Net Income (Loss) Available to Common Stockholders, Basic										460,220	353,634
Net earnings allocated to common shares										$ 460,220	$ 353,634	$ 348,178
Weighted-average basic shares and unvested restricted stock outstanding										125,100	123,060	121,670
Less: weighted-average unvested restricted stock outstanding										(1,460)	(1,447)	(1,431)
Weighted-average basic shares outstanding										123,640	121,613	120,239
Earnings Per Share, Basic (usd per share)										$ 3.72	$ 2.91	$ 2.90
Diluted income per share (usd per share)		$ 0.93	$ 0.94	$ 0.92	$ 0.93	$ 0.66	$ 0.84	$ 0.77	$ 0.65	$ 3.72	$ 2.91	$ 2.90

[1] Represents cash dividends paid to holders of unvested restricted stock, net of forfeitures, plus undistributed earnings amounts available to holders of unvested restricted stock, if any.