Earnings Per Share (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands		3 Months Ended								12 Months Ended
		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, 2017	Dec. 31, 2016	Dec. 31, 2015
Earnings Per Share [Abstract]
Net earnings		$ 84,037	$ 101,466	$ 93,647	$ 78,668					$ 357,818	$ 352,166	$ 299,619
Participating Securities, Distributed and Undistributed Earnings (Loss), Basic	[1]									4,184
Net earnings from continuing operations						$ 85,647	$ 93,895	$ 82,168	$ 90,456
Undistributed Earnings (Loss) Allocated to Participating Securities, Basic	[1]										(3,988)	(2,892)
Net earnings allocated to common shares										$ 353,634	$ 348,178	$ 296,727
Weighted-average basic shares and unvested restricted stock outstanding										123,060	121,670	107,401
Less: weighted-average unvested restricted stock outstanding										(1,447)	(1,431)	(1,074)
Weighted-average basic shares outstanding										121,613	120,239	106,327
Earnings Per Share, Basic (usd per share)										$ 2.91	$ 2.90	$ 2.79
Diluted income per share (usd per share)										$ 2.91	$ 2.90	$ 2.79

[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.