Shareholders' Equity - Perpetual Preferred Shares (Details) - USD ($) $ / shares in Units, $ in Millions	1 Months Ended			12 Months Ended
	Jul. 31, 2016	Jun. 30, 2016	May 31, 2016	Dec. 31, 2016	Dec. 31, 2015
Class of Stock [Line Items]
Liquidation preference per share (in dollars per share)				$ 25
Preferred stock, change in control redemption period				120 days
Preferred shares, shares issued (in shares)				37,010,000	17,060,000
Series D Perpetual Preferred Stock
Class of Stock [Line Items]
Preferred Shares dividend rate			6.50%	6.50%
Preferred shares, shares issued (in shares)			10,750,000
Gross proceeds from issuance of Preferred shares before offering costs			$ 268.8
Adjustments to additional paid in capital, stock issued, issuance costs			$ 8.5
Series E Perpetual Preferred Stock
Class of Stock [Line Items]
Preferred Shares dividend rate	6.35%	6.35%		6.35%
Preferred shares, shares issued (in shares)		9,200,000
Gross proceeds from issuance of Preferred shares before offering costs		$ 230.0
Adjustments to additional paid in capital, stock issued, issuance costs		$ 7.5