Significant Accounting Policies (Details) $ in Thousands	Jun. 30, 2018 USD ($)	Dec. 31, 2017 USD ($)
Advances for drilling units under construction	$ 35,552	$ 0
Cumulative installment payments made to Samsung
Advances for drilling units under construction	$ 501,258
Number of vessels	2

Amount of structure or a modification to a structure under construction. Includes recently completed structures or modifications to structures that have not been placed into service.

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 360
-SubTopic 10
-Section 50
-Paragraph 1
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=6391035&loc=d3e2868-110229

Name:	us-gaap_ConstructionInProgressGross
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant