Stockholders' Equity (Dividends Declared and Paid) (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended	12 Months Ended
Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2015	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2015
Equity
Dividends declared and paid									$ 29,745	$ 26,606	$ 24,646
Cash dividends per share	$ 0.125	$ 0.125	$ 0.125	$ 0.110	$ 0.110	$ 0.110	$ 0.110	$ 0.100	$ 0.485	$ 0.430	$ 0.380

Cash outflow in the form of ordinary dividends to common shareholders, preferred shareholders and noncontrolling interests, generally out of earnings.

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 230
-SubTopic 10
-Section 45
-Paragraph 15
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=98514028&loc=d3e3291-108585

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Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration