Capital Stock - Preferred Stock (Details) - USD ($) $ / shares in Units, $ in Thousands	1 Months Ended		3 Months Ended								12 Months Ended
	Feb. 28, 2017	Oct. 31, 2016	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Class of Stock [Line Items]
Preferred Stock, shares authorized (shares)			100,000,000				100,000,000				100,000,000	100,000,000
Preferred Stock, par value (usd per share)			$ 0.01				$ 0.01				$ 0.01	$ 0.01
Issuance of preferred stock cost											$ 314,429	$ 140,065
Dividends on preferred stock			$ 9,400	$ 9,400	$ 9,400	$ 5,283	$ 2,449	$ 0	$ 0	$ 0	$ 33,484	$ 2,449	$ 0
Preferred Class B
Class of Stock [Line Items]
Preferred Stock, shares authorized (shares)	13,000,000
Preferred Stock, dividend rate (percent)	8.00%										8.00%
Sale of stock price (in USD per share)	$ 25.00
Preferred stock, redemption price per share (in USD per share)	$ 25.00
Dividends on preferred stock											$ 22,000
Preferred stock dividends declared (in USD per share)											$ 1.6833478462
Preferred Class A
Class of Stock [Line Items]
Preferred Stock, shares authorized (shares)		5,800,000
Preferred Stock, dividend rate (percent)	8.00%	8.00%									8.00%	8.00%
Preferred Stock, par value (usd per share)	$ 0.01	$ 0.01
Sale of stock price (in USD per share)	25.00	25
Preferred stock, redemption price per share (in USD per share)	25.00	$ 25
Fixed dividend amount (in USD per share)	$ 2.00
Dividends on preferred stock											$ 12,000
Preferred stock dividends declared (in USD per share)											$ 2
Preferred stock, issuance cost and discount on shares		$ 140,000
Additional Paid-in Capital
Class of Stock [Line Items]
Issuance of preferred stock cost	$ 314,000										$ 314,299	$ 140,007
London Interbank Offered Rate (LIBOR) | Preferred Class A
Class of Stock [Line Items]
Preferred stock, basis spread on variable rate	5.791%