Earnings Per Share (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended			9 Months Ended
	Sep. 30, 2017	Jun. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016
Earnings Per Share [Abstract]
Net earnings from continuing operations	$ 101,466	$ 93,647	$ 93,895	$ 273,781	$ 266,519
Less: Earnings allocated to unvested restricted stock	(1,149)	(1,080)	(1,048)	(3,239)	(2,983)
Net earnings allocated to common shares	$ 100,317	$ 92,567	$ 92,847	$ 270,542	$ 263,536
Weighted-average basic shares and unvested restricted stock outstanding (shares)	121,447	121,422	121,818	121,405	121,739
Weighted-average unvested restricted stock outstanding (shares)	(1,394)	(1,455)	(1,401)	(1,450)	(1,425)
Weighted-average basic shares outstanding (shares)	120,053	119,967	120,417	119,955	120,314
Basic net income per share (usd per share)	$ 0.84	$ 0.77	$ 0.77	$ 2.26	$ 2.19
Net earnings from continuing operations allocated to common shares	$ 100,317	$ 92,567	$ 92,847	$ 270,542	$ 263,536
Diluted net income per share (usd per share)	$ 0.84	$ 0.77	$ 0.77	$ 2.26	$ 2.19