Earnings Per Share (Details) - USD ($) $ / shares in Units, $ in Thousands		3 Months Ended								12 Months Ended			48 Months Ended
	Feb. 18, 2014	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2014	Sep. 30, 2014	Jun. 30, 2014	Mar. 31, 2014	Dec. 31, 2013	Sep. 30, 2015	Sep. 30, 2014	Sep. 30, 2013	Sep. 30, 2015
Basic Earnings per Share from Continuing Operations
Income from continuing operations										$ 315,075	$ 289,817	$ 230,698
Less: Income from continuing operations allocated to participating securities										626	711	775
Income from continuing operations available to common shareholders										$ 314,449	$ 289,106	$ 229,923
Basic weighted average shares outstanding (shares)										101,892,000	97,606,000	90,533,000
Income per share from continuing operations - basic (usd per share)										$ 3.09	$ 2.96	$ 2.54
Basic Earnings per Share from Discontinued Operations
Income from discontinued operations										$ 0	$ 0	$ 12,496
Less: Income from discontinued operations allocated to participating securities										0	0	42
Income from discontinued operations available to common shareholders										$ 0	$ 0	$ 12,454
Income (loss) from discontinued operations per share - Basic (usd per share)										$ 0.00	$ 0.00	$ 0.14
Net income per share — basic (usd per share)		$ 0.23	$ 0.55	$ 1.35	$ 0.96	$ 0.23	$ 0.45	$ 1.38	$ 0.95	$ 3.09	$ 2.96	$ 2.68
Diluted Earnings per Share from Continuing Operations
Effect of dilutive stock options and other shares										$ 0	$ 0	$ 5
Income (loss) from continuing operations available to common shareholders										$ 314,449	$ 289,106	$ 229,928
Additional dilutive stock options and other shares										0	2,000	1,178,000
Diluted weighted average shares outstanding (shares)										101,892,000	97,608,000	91,711,000
Income per share from continuing operations - diluted (usd per share)										$ 3.09	$ 2.96	$ 2.50
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	$ 0	$ 12,454
Additional dilutive stock options and other shares										0	2,000	1,178,000
Diluted weighted average shares outstanding										101,892,000	97,608,000	91,711,000
Income per share from discontinued operations - diluted (usd per share)										$ 0.00	$ 0.00	$ 0.14
Net income per share — diluted (usd per share)		$ 0.23	$ 0.55	$ 1.35	$ 0.96	$ 0.23	$ 0.45	$ 1.38	$ 0.95	$ 3.09	$ 2.96	$ 2.64
Earnings Per Share Diluted Other Disclosures Abstract
Anti-dilutive stock options excluded from computation of diluted earnings per share												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									$ 0	$ 390,205	$ 0
Share Price	$ 44.00
Stock Repurchase Program [Abstract]
Stock Repurchased During Period, Shares													387,991
Stock Repurchased During Period, Value													$ 12,500
Summary Of Stock Option Activity [Abstract]
Share-based Compensation Arrangement by Share-based Payment Award, Options, Exercisable, Number		0				0				0	0		0