The maximum number of shares (or other type of equity) originally approved (usually by shareholders and board of directors), net of any subsequent amendments and adjustments, for awards under the equity-based compensation plan. As stock or unit options and equity instruments other than options are awarded to participants, the shares or units remain authorized and become reserved for issuance under outstanding awards (not necessarily vested).

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)(3)
-URI http://asc.fasb.org/extlink&oid=109197908&loc=d3e5070-113901

Name:	us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfSharesAuthorized
Namespace Prefix:	us-gaap_
Data Type:	xbrli:sharesItemType
Balance Type:	na
Period Type:	instant

Events Subsequent to Original Issuance of Condensed Consolidated Financial Statements (unaudited) (Details) - $ / shares	3 Months Ended	12 Months Ended
	Mar. 31, 2019	Dec. 31, 2017	Dec. 31, 2016	Jun. 30, 2019	Apr. 03, 2019
Subsequent Event [Line Items]
Exercise price (in USD per share)	$ 11.29	$ 6.51	$ 6.54
2019 Stock Option Plan
Subsequent Event [Line Items]
Shares of common stock reserved for issuance (in shares)	2,317,000
2019 Stock Option Plan \| Subsequent Event
Subsequent Event [Line Items]
Shares of common stock reserved for issuance (in shares)				36,982	687,176