Stockholders' Equity (Details) - USD ($) $ / shares in Units, $ in Thousands	1 Months Ended	3 Months Ended		12 Months Ended
	Apr. 30, 2020	Mar. 31, 2020	Mar. 31, 2019	Dec. 31, 2019	Feb. 28, 2018
Class of Stock [Line Items]
Total allowable shares (in shares)		375,000,000		375,000,000
Net proceeds		$ 696	$ 5,279
Total shares issued (in shares)		171,963,354		171,694,209
Common stock dividends		$ 88,148	$ 80,566
Common stock dividends per share (in dollars per share)		$ 0.515	$ 0.500
Common stock dividends declared (in dollars per share)		$ 0.515	$ 0.50
Subsequent event
Class of Stock [Line Items]
Common stock dividends declared (in dollars per share)	$ 0.515
Series E Preferred Stock
Class of Stock [Line Items]
Preferred stock dividends		$ 0	$ 4,097
Preferred stock dividends per depositary share (in dollars per share)		$ 0	$ 0.356250
Dividend rate		5.70%
Series F Preferred Stock
Class of Stock [Line Items]
Preferred stock dividends		$ 4,485	$ 4,485
Preferred stock dividends per depositary share (in dollars per share)		$ 0.325000	$ 0.325000
Dividend rate		5.20%		5.20%
DRIP
Class of Stock [Line Items]
Total allowable shares (in shares)					10,000,000
Shares of common stock (in shares)		12,528	101,180
Net proceeds		$ 696	$ 5,279
ATM equity program
Class of Stock [Line Items]
Total allowable shares (in shares)		12,000,000
Total shares issued (in shares)		9,722,185