Shareholders' Equity - Cash Dividends Declared Per Common Share (Details) - $ / shares	3 Months Ended	12 Months Ended
Dec. 31, 2018	Dec. 31, 2016	Dec. 31, 2012	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Disclosure Shareholders Equity [Abstract]
Quarterly dividend declared and paid per common share	$ 0.60	$ 0.55	$ 0.58	$ 2.4	$ 2.32	$ 2.2

Aggregate dividends paid 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

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