Stockholders' Equity - Schedule of Repurchase Prices Under Share Repurchase Plan (Footnote) (Details)	12 Months Ended
Dec. 31, 2017
Share Repurchase Plan [Member] \| Common Stock [Member]
Class of Stock [Line Items]
Required holding period to be eligible to redeem shares under share repurchase plan	1 year

Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

No definition available.

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Namespace Prefix:	us-gaap_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration