Stock-Based Compensation - Nonvested Stock Awards (Narrative) (Details)	12 Months Ended
Dec. 31, 2018
Employees
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Vesting period	3 years
Directors
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Vesting period	1 year

Period which an employee's right to exercise an award is no longer contingent on satisfaction of either a service condition, market condition or a performance condition, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 718
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (a)(1)
-URI http://asc.fasb.org/extlink&oid=109197908&loc=d3e5070-113901

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