Shareholders' Equity - Perpetual Preferred Shares (Details) - USD ($) $ / shares in Units, $ in Thousands	1 Months Ended		3 Months Ended	6 Months Ended
	Jun. 30, 2016	May 31, 2016	Jun. 30, 2016	Jun. 30, 2016	Jun. 30, 2015	Dec. 31, 2015
Class of Stock [Line Items]
Liquidation preference (in USD per share)	$ 25		$ 25	$ 25
Gross proceeds from issuance of preferred stock				$ 482,726	$ 0
Preferred stock change in control redemption period				120 days
Preferred shares, shares issued	37,010,000		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		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%
Gross proceeds from issuance of preferred stock	$ 230,000
Preferred shares, shares issued	9,200,000		9,200,000	9,200,000
Issuance of perpetual preferred shares, offering costs	$ 7,500