Shareholders' Equity - Perpetual Preferred Shares (Details) - USD ($) $ / shares in Units, $ in Thousands	1 Months Ended			3 Months Ended	9 Months Ended
	Jul. 31, 2016	Jun. 30, 2016	May 31, 2016	Sep. 30, 2016	Sep. 30, 2016	Sep. 30, 2015	Dec. 31, 2015
Class of Stock [Line Items]
Liquidation preference (in USD per share)				$ 25	$ 25
Preferred stock change in control redemption period					120 days
Gross proceeds from issuance of preferred stock					$ 498,750	$ 0
Preferred shares, shares issued (in shares)				37,010,000	37,010,000		17,060,000
Series D Perpetual Preferred Shares
Class of Stock [Line Items]
Preferred stock, dividend rate, percentage			6.50%	6.50%	6.50%
Gross proceeds from issuance of preferred stock			$ 268,800
Preferred shares, shares issued (in shares)			10,750,000
Issuance of perpetual preferred shares, offering costs			$ 8,500
Series E Perpetual Preferred Shares
Class of Stock [Line Items]
Preferred stock, dividend rate, percentage	6.35%	6.35%		6.35%	6.35%
Gross proceeds from issuance of preferred stock		$ 230,000
Preferred shares, shares issued (in shares)		9,200,000
Issuance of perpetual preferred shares, offering costs		$ 7,500