Summary of Significant Accounting Policies - Earnings Per Share (Details) - shares	3 Months Ended
Mar. 31, 2019	Mar. 31, 2018
Accounting Policies [Abstract]
Number of shares of common stock received for each exchangeable share (in shares)	1
Weighted average shares outstanding attributable to participating securities (in shares)	2,800,000	2,700,000

This element represents nonvested share-based payment awards that contain non-forfeitable rights to dividends or dividend equivalents (whether paid or unpaid). Basic and dilutive earnings per share are generally disclosed for such shares using the two-class method.

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 260
-SubTopic 10
-Section 45
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Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
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Reference 4: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
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Reference 5: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 260
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-Section 45
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-URI http://asc.fasb.org/extlink&oid=109260490&loc=SL5780132-109256

Name:	us-gaap_IncrementalCommonSharesAttributableToParticipatingNonvestedSharesWithNonForfeitableDividendRights
Namespace Prefix:	us-gaap_
Data Type:	xbrli:sharesItemType
Balance Type:	na
Period Type:	duration