Stockholders' Equity (Details) - Common Stock - $ / shares				9 Months Ended
Aug. 31, 2018	May 24, 2018	Mar. 09, 2018	Sep. 30, 2018
Stockholders' Equity
Dividends Payable, Date of Record	Sep. 28, 2018	Jun. 29, 2018	Mar. 29, 2018
Common Stock dividend declared (per share)	$ 1.03	$ 1.03	$ 0.98	$ 3.04

Aggregate dividends declared during the period for each share of common stock outstanding.

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 505
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.3-04)
-URI http://asc.fasb.org/extlink&oid=27012166&loc=d3e187085-122770

Name:	us-gaap_CommonStockDividendsPerShareDeclared
Namespace Prefix:	us-gaap_
Data Type:	num:perShareItemType
Balance Type:	na
Period Type:	duration