Capital Stock - Preferred Stock (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019
Class of Stock [Line Items]
Dividends on preferred stock	$ 18,438	$ 18,438	$ 36,875	$ 35,829
Series A Preferred Stock
Class of Stock [Line Items]
Dividends on preferred stock	$ 3,000	$ 6,000	$ 6,000
Preferred stock dividends declared (in USD per share)	$ 0.50	$ 1.00	$ 1.00
Series B Preferred Stock
Class of Stock [Line Items]
Dividends on preferred stock	$ 7,000	$ 13,000	$ 13,000
Preferred stock dividends declared (in USD per share)	$ 0.50	$ 1.00	$ 1.00
Series C Preferred Stock
Class of Stock [Line Items]
Dividends on preferred stock	$ 5,000	$ 10,000	$ 10,000
Preferred stock dividends declared (in USD per share)	$ 0.48	$ 0.97	$ 0.97
Series D Preferred Stock
Class of Stock [Line Items]
Dividends on preferred stock	$ 4,000	$ 7,000	$ 8,000
Preferred stock dividends declared (in USD per share)	$ 0.50	$ 0.87	$ 1.00