Shareholders' Equity - At the Market Common Share Offering Program (Details) - USD ($)	1 Months Ended	12 Months Ended
	Aug. 31, 2014	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014	Nov. 30, 2016
Class of Stock [Line Items]
Proceeds from issuance of Class A common shares		$ 102,830,000	$ 0	$ 308,435,000
Class A common shares
Class of Stock [Line Items]
Common shares, shares issued (in shares)		242,740,482	207,235,510
Proceeds from issuance of Class A common shares	$ 313,300,000
Stock issuance costs	$ 4,900,000	$ 227,000	$ 0	$ 0
At the Market - Common Share Offering Program | Class A common shares
Class of Stock [Line Items]
Common shares, shares issued (in shares)		4,900,000
Proceeds from issuance of Class A common shares		$ 104,000,000
Sale of stock, price per share (in dollars per share)		$ 21.13
Proceeds from sale of stock, net of issuance costs		$ 102,800,000
Stock issuance costs		1,200,000
Shares reserved for future issuance					$ 400,000,000.0
Remaining available for future shares		$ 296,000,000