Earnings Per Share (Details) (USD $) In Thousands, except Share data, unless otherwise specified	0 Months Ended	3 Months Ended		6 Months Ended
	Feb. 18, 2014	Mar. 31, 2015	Mar. 31, 2014	Mar. 31, 2015	Mar. 31, 2014	Feb. 18, 2014
Earnings Per Share [Abstract]
Net income (loss)		$ 137,684	$ 133,367	$ 235,279	$ 220,383
Stock Issued During Period, Shares, New Issues	9,200,000
Shares Issued At Overallotment Option	1,200,000
Share Price						$ 44.00
Net proceeds from equity offering	390,200			0	390,205
Basic Earnings per Share from Continuing Operations
Undistributed Earnings (Loss) Allocated to Participating Securities, Basic		296	334	520	572
Income from continuing operations available to common shareholders		137,388	133,033	234,759	219,811
Basic weighted average shares outstanding		101,746,000	96,174,000	101,667,000	94,013,000
Net income per share - Basic		$ 1.35	$ 1.38	$ 2.31	$ 2.34
Diluted Earnings per Share from Continuing Operations
Income from continuing operations available to common shareholders		137,388	133,033	234,759	219,811
Effect of dilutive stock options and other shares		0	0	0	0
Income from continuing operations available to common shareholders		$ 137,388	$ 133,033	$ 234,759	$ 219,811
Basic weighted average shares outstanding		101,746,000	96,174,000	101,667,000	94,013,000
Additional dilutive stock options and other shares		0	2,000	0	2,000
Diluted weighted average shares outstanding		101,746,000	96,176,000	101,667,000	94,015,000
Net income per share - Diluted		$ 1.35	$ 1.38	$ 2.31	$ 2.34
Earnings Per Share Diluted Other Disclosures Abstract
Anti-dilutive stock options excluded from computation of diluted earnings per share (in shares)			0		0
Share Repurchase Program - Shares Purchased				0	0
Summary of Stock Option Activity [Abstract]
Share-based Compensation Arrangement by Share-based Payment Award, Options, Exercisable, Number		0		0