Summary of Significant Accounting Policies - Cost Method Investment (Details) - USD ($) $ in Millions	Dec. 31, 2016	Dec. 31, 2015
Schedule of Cost-method Investments [Line Items]
Amount	$ 39.8	$ 6.2
Colonial
Schedule of Cost-method Investments [Line Items]
Ownership	6.00%	3.00%
Amount	$ 11.4	$ 6.2
Explorer
Schedule of Cost-method Investments [Line Items]
Ownership	2.62%	0.00%
Amount	$ 26.3	$ 0.0
Cleopatra
Schedule of Cost-method Investments [Line Items]
Ownership	1.00%	0.00%
Amount	$ 2.1

Amount, after adjustment, of cost-method investment. Adjustments include, but are not limited to, dividends received in excess of earnings after date of investment that are considered a return of investment and other than temporary impairments.

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.5-02.12)
-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 325
-SubTopic 20
-Section 50
-Paragraph 1
-URI http://asc.fasb.org/extlink&oid=6872867&loc=d3e40691-111596

Reference 3: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 325
-SubTopic 20
-Section 35
-Paragraph 2
-URI http://asc.fasb.org/extlink&oid=29638308&loc=d3e40346-111594

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