Equity - Preferred Stock (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended			9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018		Sep. 30, 2019	Sep. 30, 2018
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Preferred stock, shares outstanding, beginning balance (shares)				5,603,458
Preferred stock, shares outstanding, ending balance (shares)	5,563,458			5,563,458
5.75%
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Preferred stock, shares outstanding, beginning balance (shares)	770,000	770,000		770,000	770,000
Preferred stock, shares outstanding, ending balance (shares)	770,000	770,000		770,000	770,000
Liquidation price per share (in dollars per share)	$ 1,000			$ 1,000
5.75% (A)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Preferred stock, shares outstanding, beginning balance (shares)	463,000	463,000		463,000	463,000
Preferred stock, shares outstanding, ending balance (shares)	423,000	463,000		423,000	463,000
Liquidation price per share (in dollars per share)	$ 1,000			$ 1,000
4.50%
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Preferred stock, shares outstanding, beginning balance (shares)	2,559,000	2,559,000		2,559,000	2,559,000
Preferred stock, shares outstanding, ending balance (shares)	2,559,000	2,559,000		2,559,000	2,559,000
Liquidation price per share (in dollars per share)	$ 100			$ 100
5.00% (2005B)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Preferred stock, shares outstanding, beginning balance (shares)	1,811,000	1,811,000		1,811,000	1,811,000
Preferred stock, shares outstanding, ending balance (shares)	1,811,000	1,811,000		1,811,000	1,811,000
Liquidation price per share (in dollars per share)	$ 100			$ 100
PREFERRED STOCK
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Exchange of preferred stock	$ (40,000)	$ 0	[1]	$ (40,000)	$ 0	[1]
PREFERRED STOCK | 5.75%
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Exchange of preferred stock	0			0
PREFERRED STOCK | 5.75% (A)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Exchange of preferred stock	$ (40)			$ (40)
Interest rate, stated percentage	5.75%			5.75%
PREFERRED STOCK | 4.50%
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Exchange of preferred stock	$ 0			$ 0
PREFERRED STOCK | 5.00% (2005B)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Exchange of preferred stock	$ 0			$ 0

[1] Financial information for prior periods has been recast to reflect the retrospective application of the successful efforts method of accounting. See Note 1.