Unsecured Senior Notes (Details)	3 Months Ended
	Mar. 31, 2021 USD ($) item $ / shares	Mar. 31, 2020 USD ($)	Dec. 31, 2020 USD ($)	Mar. 29, 2017 USD ($)
Unsecured Senior Notes
Interest expense	$ 103,374,000	$ 120,025,000
Add: Loss on extinguishment of Convertible Notes	(516,000)	(170,000)
Principal amount of notes, basis for conversion	$ 1,000
Closing share price (in dollars per share) | $ / shares	$ 24.74
Conversion upon satisfaction of closing market price condition | Minimum
Unsecured Senior Notes
Period of average closing market price of common stock as a basis for debt conversion	10 days
2021 Senior Notes 5.00%
Unsecured Senior Notes
Coupon Rate (as a percent)	5.00%
Effective Rate (as a percent)	5.32%
Remaining Period of Amortization	8 months 12 days
Principal Amount	$ 700,000,000		$ 700,000,000
Senior Notes 2023
Unsecured Senior Notes
Coupon Rate (as a percent)	5.50%
Effective Rate (as a percent)	5.71%
Remaining Period of Amortization	2 years 7 months 6 days
Principal Amount	$ 300,000,000		300,000,000
2023 Convertible Notes
Unsecured Senior Notes
Coupon Rate (as a percent)	4.38%			4.375%
Effective Rate (as a percent)	4.57%
Remaining Period of Amortization	2 years
Principal Amount	$ 250,000,000		250,000,000
Amount issued				$ 250,000,000.0
Conversion Rate	38.5959
Conversion price (in dollars per share) | $ / shares	$ 25.91
Closing share price (in dollars per share) | $ / shares	$ 24.74
If-converted value	$ 238,700,000
Amount by which if-converted value of the Notes are less than principal amount	11,300,000
Convertible notes fair value	255,800,000
Convertible notes carrying value	$ 248,600,000
2025 Senior Notes
Unsecured Senior Notes
Coupon Rate (as a percent)	4.75%
Effective Rate (as a percent)	5.04%
Remaining Period of Amortization	4 years
Principal Amount	$ 500,000,000		500,000,000
2025 Senior Notes | LIBOR
Unsecured Senior Notes
Pricing margin (as a percent)	2.53%
Principal Amount	$ 470,000,000.0
Unsecured Senior Notes
Unsecured Senior Notes
Principal Amount	1,750,000,000		1,750,000,000
Unamortized deferred financing costs	(5,076,000)		(5,589,000)
Carrying amount of conversion option equity components recorded in additional paid-in capital for outstanding convertible notes			3,755,000
Carrying amount of debt components	1,735,658,000		1,732,520,000
Convertible Senior Notes
Unsecured Senior Notes
Unamortized discount	(910,000)		(2,559,000)
Interest expense	$ 2,900,000	$ 3,000,000.0
Minimum number of conditions to be satisfied for conversion of debt | item	1
Convertible Senior Notes | Conversion upon satisfaction of closing market price condition
Unsecured Senior Notes
Minimum trading period as a basis for debt conversion	20 days
Consecutive trading period as a basis for debt conversion	30 days
Convertible Senior Notes | Conversion upon satisfaction of closing market price condition | Minimum
Unsecured Senior Notes
Percentage of per share value of distributions that exceeds the market price of the entity's common stock as a basis for debt conversion	10.00%
Convertible Senior Notes | Conversion upon satisfaction of trading price condition
Unsecured Senior Notes
Consecutive trading period as a basis for debt conversion	5 days
Convertible Senior Notes | Conversion upon satisfaction of trading price condition | Maximum
Unsecured Senior Notes
Percentage of conversion price and last reported sales price as a basis for debt conversion	98.00%
Senior Notes
Unsecured Senior Notes
Unamortized discount	$ (8,356,000)		$ (9,332,000)
Convertible Notes and Senior Notes | 2017 Notes | Conversion upon satisfaction of closing market price condition | Minimum
Unsecured Senior Notes
Percentage of conversion price as a basis for debt conversion	110.00%