Stockholders' Equity of the Company - Narrative (Details) - USD ($)			1 Months Ended		12 Months Ended
	Aug. 15, 2017	Mar. 30, 2017	Jul. 31, 2019	Aug. 31, 2018	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017	Jun. 30, 2018
Class of Stock [Line Items]
Common stock, value, issued					$ 1,060,000	$ 1,007,000
Aggregate net proceeds after selling commissions					$ 353,722,000	$ 130,693,000	$ 326,058,000
Sale of stock, shares issued (in shares)					106,016,287	100,746,988
Stock repurchase program, number of shares authorized to be repurchased					4,935,826
Original issuance costs					$ 0	$ 0	7,589,000
2014 At-The-Market Program [Member]
Class of Stock [Line Items]
Aggregate gross proceeds						$ 300,000,000.0
2018 At-The-Market Program [Member]
Class of Stock [Line Items]
Aggregate gross proceeds								$ 500,000,000.0
Series H Preferred Stock [Member]
Class of Stock [Line Items]
Preferred stock (in shares)	4,000,000	4,000,000
Preferred stock, dividend rate	6.375%
Preferred stock, liquidation preference per share (in dollars per share)	$ 25.00
Preferred stock liquidation preference	$ 100,000,000.0
Series G Preferred Stock [Member]
Class of Stock [Line Items]
Preferred stock (in shares)		4,000,000
Preferred stock, dividend rate		6.875%
Preferred stock, liquidation preference per share (in dollars per share)		$ 25.00
Preferred stock liquidation preference		$ 100,000,000.0
Series G And H Preferred Stock [Member]
Class of Stock [Line Items]
Original issuance costs							$ 7,600,000
Forward Equity Offering [Member]
Class of Stock [Line Items]
Common stock, value, issued				$ 360,500,000
Stock issued, price per share (in dollar per share)				$ 72.10
Aggregate net proceeds after selling commissions			$ 354,300,000
Forward Equity Offering [Member] | Common Stock [Member]
Class of Stock [Line Items]
Stock issued (in shares)			5,000,000	5,000,000
Aggregate net proceeds after selling commissions			$ 354,300,000
Sale of stock, shares issued (in shares)			5,000,000
Forward Equity Offering [Member] | Common Stock [Member] | 2014 At-The-Market Program [Member]
Class of Stock [Line Items]
Sale of stock, shares available for sale (in shares)						1,369,729
Forward Equity Offering [Member] | Common Stock [Member] | 2018 At-The-Market Program [Member]
Class of Stock [Line Items]
Stock issued, price per share (in dollar per share)					$ 80.08
Sale of stock, shares available for sale (in shares)					3,147,110
Sale of stock, shares issued (in shares)					447,466	447,466
Sale of stock, available for sale under program					$ 214,200,000