Fair Value Measurements - Textual (Details) - USD ($)	1 Months Ended	12 Months Ended
Dec. 31, 2009	Dec. 31, 2016
Investment [Line Items]
Level 1 to Level 2 transfers		$ 0
Common shares of CO2 Solutions
Investment [Line Items]
Number of Common Shares Fair Value	10,000,000
Common shares of CO2 Solutions
Investment [Line Items]
Number of Common Shares Fair Value		10,000,000

Amount of transfers of assets measured on a recurring basis out of Level 1 of the fair value hierarchy into Level 2.

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 820
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (bb)
-URI http://asc.fasb.org/extlink&oid=66048111&loc=d3e19207-110258

Name:	us-gaap_FairValueAssetsLevel1ToLevel2TransfersAmount
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant