Number of operating segments. An operating segment is a component of an enterprise: (a) that engages in business activities from which it may earn revenues and incur expenses (including revenues and expenses relating to transactions with other components of the same enterprise), (b) whose operating results are regularly reviewed by the enterprise's chief operating decision maker to make decisions about resources to be allocated to the segment and assess its performance, and (c) for which discrete financial information is available. An operating segment may engage in business activities for which it has yet to earn revenues, for example, start-up operations may be operating segments before earning revenues.

No definition available.

Name:	us-gaap_NumberOfOperatingSegments
Namespace Prefix:	us-gaap_
Data Type:	xbrli:integerItemType
Balance Type:	na
Period Type:	duration

Significant Accounting Policies, Convertible Debt and Segment Information (Details) - Segment	1 Months Ended		6 Months Ended
	Jul. 31, 2017	Jul. 19, 2017	Jun. 30, 2017	Dec. 31, 2016
Segment Information [Abstract]
Number of operating segments			2
Percentage ownership before IPO			100.00%
Subsequent Event [Member]
Segment Information [Abstract]
Percentage ownership after IPO	68.00%	68.00%
1 Percent Convertible Senior Notes [Member]
Convertible Debt [Abstract]
Interest rate on convertible senior notes			1.00%	1.00%
2 3/4 Percent Convertible Senior Notes [Member]
Convertible Debt [Abstract]
Interest rate on convertible senior notes			2.75%