Condensed Consolidated Balance Sheets (Parenthetical) - shares	Mar. 31, 2019	Dec. 31, 2018
Common Class A
Common shares issued (in shares)	68,746,555	66,810,980
Common shares outstanding (in shares)	68,746,555	66,810,980
Common Class B
Common shares issued (in shares)	79,275,234	78,838,736
Common shares outstanding (in shares)	79,275,234	78,838,736

Total number of common shares of an entity that have been sold or granted to shareholders (includes common shares that were issued, repurchased and remain in the treasury). These shares represent capital invested by the firm's shareholders and owners, and may be all or only a portion of the number of shares authorized. Shares issued include shares outstanding and shares held in the treasury.

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.5-02(29))
-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682

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