Earnings Per Share (Details) (USD $)	0 Months Ended	3 Months Ended								12 Months Ended
	Feb. 18, 2014	Sep. 30, 2014	Jun. 30, 2014	Mar. 31, 2014	Dec. 31, 2013	Sep. 30, 2013	Jun. 30, 2013	Mar. 31, 2013	Dec. 31, 2012	Sep. 30, 2014	Sep. 30, 2013	Sep. 30, 2012	Feb. 18, 2014
Basic Earnings per Share from Continuing Operations
Income from continuing operations						$ 7,536,000	$ 33,474,000	$ 112,340,000	$ 77,348,000	$ 289,817,000	$ 230,698,000	$ 192,196,000
Less: Income from continuing operations allocated to participating securities										711,000	775,000	793,000
Income from continuing operations available to common shareholders										289,106,000	229,923,000	191,403,000
Basic weighted average shares outstanding (shares)										97,606,000	90,533,000	90,150,000
Income per share from continuing operations - basic (usd per share)						$ 0.08	$ 0.37	$ 1.24	$ 0.85	$ 2.96	$ 2.54	$ 2.12
Basic Earnings per Share from Discontinued Operations
Income from discontinued operations										0	12,496,000	24,521,000
Less: Income from discontinued operations allocated to participating securities										0	42,000	101,000
Income from discontinued operations available to common shareholders										0	12,454,000	24,420,000
Income (loss) from discontinued operations per share - Basic (usd per share)						$ 0.00	$ 0.06	$ 0.04	$ 0.04	$ 0.00	$ 0.14	$ 0.27
Net income per share — basic (usd per share)		$ 0.23	$ 0.45	$ 1.38	$ 0.94	$ 0.08	$ 0.43	$ 1.28	$ 0.89	$ 2.96	$ 2.68	$ 2.39
Diluted Earnings per Share from Continuing Operations
Effect of dilutive stock options and other shares										0	5,000	4,000
Income (loss) from continuing operations available to common shareholders										289,106,000	229,928,000	191,407,000
Additional dilutive stock options and other shares										2,000	1,178,000	1,022,000
Diluted weighted average shares outstanding (shares)										97,608,000	91,711,000	91,172,000
Income per share from continuing operations - diluted (usd per share)						$ 0.08	$ 0.36	$ 1.23	$ 0.85	$ 2.96	$ 2.50	$ 2.10
Diluted Earnings per Share from Discontinued Operations
Effect of dilutive stock options and other shares										0	0	0
Income from discontinued operations available to common shareholders										0	12,454,000	24,420,000
Additional dilutive stock options and other shares										2,000	1,178,000	1,022,000
Diluted weighted average shares outstanding										97,608,000	91,711,000	91,172,000
Income per share from discontinued operations - diluted (usd per share)						$ 0.00	$ 0.06	$ 0.04	$ 0.03	$ 0.00	$ 0.14	$ 0.27
Net income per share — diluted (usd per share)		$ 0.23	$ 0.45	$ 1.38	$ 0.94	$ 0.08	$ 0.42	$ 1.27	$ 0.88	$ 2.96	$ 2.64	$ 2.37
Earnings Per Share Diluted Other Disclosures Abstract
Anti-dilutive stock options excluded from computation of diluted earnings per share											0	0
Stock Issued During Period, Shares, New Issues	9,200,000
Shares Issued At Overallotment Option	1,200,000
Net proceeds from equity offering	390,200,000									390,205,000	0	0
Share Price													$ 44.00
Stock Repurchase Program [Abstract]
Stock Repurchased During Period, Shares												387,991
Stock Repurchased During Period, Value										$ 12,500,000
Summary Of Stock Option Activity [Abstract]
Share-based Compensation Arrangement by Share-based Payment Award, Options, Exercisable, Number		0								0