Capital Stock - Preferred Stock (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended
	Mar. 31, 2020	Mar. 31, 2019
Class of Stock [Line Items]
Dividends on preferred stock	$ 18,438	$ 17,392
Series A Preferred Stock
Class of Stock [Line Items]
Dividends on preferred stock	$ 3,000	$ 3,000
Preferred stock dividends declared (in USD per share)	$ 0.50	$ 0.50
Series B Preferred Stock
Class of Stock [Line Items]
Dividends on preferred stock	$ 7,000	$ 7,000
Preferred stock dividends declared (in USD per share)	$ 0.50	$ 0.50
Series C Preferred Stock
Class of Stock [Line Items]
Dividends on preferred stock	$ 5,000	$ 5,000
Preferred stock dividends declared (in USD per share)	$ 0.48	$ 0.48
Series D Preferred Stock
Class of Stock [Line Items]
Dividends on preferred stock	$ 4,000
Preferred stock dividends declared (in USD per share)	$ 0.50