Earnings Per Share (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands		3 Months Ended								12 Months Ended
		Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Earnings Per Share [Abstract]
Net earnings		$ 85,647	$ 93,895	$ 82,168	$ 90,456					$ 352,166	$ 299,619	$ 168,905
Participating Securities, Distributed and Undistributed Earnings (Loss), Basic										3,988
Net earnings from continuing operations						$ 71,841	$ 69,616	$ 85,083	$ 73,079	352,166	299,619	170,468
Undistributed Earnings (Loss) Allocated to Participating Securities, Basic	[1]										(2,892)	(1,959)
Net earnings from continuing operations allocated to common shares										348,178	296,727	168,509
Net loss from discontinued operations allocated to common shares										0	0	(1,545)
Net earnings allocated to common shares										$ 348,178	$ 296,727	$ 166,964
Weighted-average basic shares and unvested restricted stock outstanding										121,670	107,401	87,871
Less: weighted-average unvested restricted stock outstanding										(1,431)	(1,074)	(1,018)
Weighted-average basic shares outstanding										120,239	106,327	86,853
Net earnings from continuing operations										$ 2.90	$ 2.79	$ 1.94
Net loss from discontinued operations										0.00	0.00	(0.02)
Basic net income per share (usd per share)										$ 2.90	$ 2.79	$ 1.92
Net earnings allocated to common shares										348,178	296,727	166,964
Net earnings from continuing operations										$ 2.90	$ 2.79	$ 1.94
Net loss from discontinued operations										0.00	0.00	(0.02)
Diluted net income per share (usd per share)		$ 0.71	$ 0.77	$ 0.68	$ 0.74	$ 0.60	$ 0.68	$ 0.83	$ 0.71	$ 2.90	$ 2.79	$ 1.92

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