Unsecured Secured Notes (Details) $ / shares in Units, shares in Thousands			3 Months Ended		9 Months Ended
	Mar. 29, 2017 USD ($)	Dec. 16, 2016 USD ($)	Sep. 30, 2017 USD ($) $ / shares shares	Sep. 30, 2016 USD ($) $ / shares shares	Sep. 30, 2017 USD ($) item $ / shares shares	Sep. 30, 2016 USD ($) $ / shares shares	Dec. 31, 2016 USD ($)	Oct. 08, 2014 USD ($)	Jul. 03, 2013 USD ($)	Feb. 15, 2013 USD ($)
Convertible Senior Notes
Principal Amount			$ 2,073,229,000		$ 2,073,229,000		$ 2,053,229,000
Conversion Spread Value - Shares | shares			2,313	3,445	2,284	3,766
Unamortized deferred financing costs			$ (6,018,000)		$ (6,018,000)		(5,822,000)
Carrying amount of debt components			2,044,523,000		2,044,523,000		2,011,544,000
Carrying amount of conversion option equity components recorded in additional paid-in capital			31,638,000		31,638,000		45,988,000
Principal amount of notes, basis for conversion			$ 1,000		$ 1,000
Closing share price (in dollars per share) | $ / shares			$ 21.72	$ 22.52	$ 21.72	$ 22.52
Loss on extinguishment of debt					$ 5,916,000
Conversion upon satisfaction of closing market price condition
Convertible Senior Notes
Minimum number of conditions to be satisfied for conversion of debt | item					1
Minimum trading period as a basis for debt conversion					20 days
Consecutive trading period as a basis for debt conversion					30 days
Conversion upon satisfaction of closing market price condition | Minimum
Convertible 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%
Conversion upon satisfaction of closing market price condition | Maximum
Convertible Senior Notes
Period of average closing market price of common stock as a basis for debt conversion					10 days
Conversion upon satisfaction of trading price condition
Convertible Senior Notes
Consecutive trading period as a basis for debt conversion					5 days
Conversion upon satisfaction of trading price condition | Maximum
Convertible Senior Notes
Percentage of conversion price and last reported sales price as a basis for debt conversion					98.00%
2017 Notes
Convertible Senior Notes
Amount issued								$ 431,300,000
Principal Amount			$ 411,885,000		$ 411,885,000		411,885,000
Coupon Rate (as a percent)			3.75%		3.75%			3.75%
Effective Rate (as a percent)			5.87%		5.87%
Remaining Period of Amortization					0 years
Conversion Rate					41.7397
Conversion price (in dollars per share) | $ / shares			$ 23.96		$ 23.96
Amount by which if-converted value of the Notes are less than principal amount					$ 38,500,000
2018 Notes
Convertible Senior Notes
Amount issued										$ 600,000,000
Principal Amount			$ 369,981,000		$ 369,981,000		599,981,000
Coupon Rate (as a percent)			4.55%		4.55%					4.55%
Effective Rate (as a percent)			6.10%		6.10%
Remaining Period of Amortization					4 months 24 days
Conversion Rate					48.0666
Conversion price (in dollars per share) | $ / shares			$ 20.80		$ 20.80
Conversion Spread Value - Shares | shares			742	1,595	733	1,743
Amount by which if-converted value of the Notes exceed principal amount					$ 16,400,000
2019 Notes
Convertible Senior Notes
Amount issued									$ 460,000,000
Principal Amount			$ 341,363,000		$ 341,363,000		341,363,000
Coupon Rate (as a percent)			4.00%		4.00%				4.00%
Effective Rate (as a percent)			5.35%		5.35%
Remaining Period of Amortization					1 year 3 months 18 days
Conversion Rate					50.7031
Conversion price (in dollars per share) | $ / shares			$ 19.72		$ 19.72
Conversion Spread Value - Shares | shares			1,571	1,850	1,551	2,023
Amount by which if-converted value of the Notes exceed principal amount					$ 34,600,000
2019 Notes | Conversion upon satisfaction of closing market price condition | Minimum
Convertible Senior Notes
Percentage of conversion price as a basis for debt conversion					130.00%
2021 Senior Notes
Convertible Senior Notes
Amount issued		$ 700,000,000
Principal Amount			$ 700,000,000		$ 700,000,000		700,000,000
Coupon Rate (as a percent)		5.00%	5.00%		5.00%
Effective Rate (as a percent)			5.32%		5.32%
Remaining Period of Amortization					4 years 2 months 12 days
2021 Senior Notes | Debt instrument redemption period one
Convertible Senior Notes
Percentage of principal amount that may be redeemed		100.00%
2021 Senior Notes | Debt instrument redemption period two
Convertible Senior Notes
Percentage of principal amount that may be redeemed		35.00%
2023 Notes
Convertible Senior Notes
Principal Amount			$ 250,000,000		$ 250,000,000
Coupon Rate (as a percent)			4.38%		4.38%
Effective Rate (as a percent)			4.86%		4.86%
Remaining Period of Amortization					5 years 6 months
Conversion Rate					38.5959
Conversion price (in dollars per share) | $ / shares			$ 25.91		$ 25.91
Amount by which if-converted value of the Notes are less than principal amount					$ 40,400,000
Portion of repurchase price attributable to equity component recognized as a reduction of additional paid-in-capital					$ 3,755,000
2023 Notes | Conversion upon satisfaction of closing market price condition | Minimum
Convertible Senior Notes
Percentage of conversion price as a basis for debt conversion					110.00%
Convertible Senior Notes
Convertible Senior Notes
Unamortized discount			$ (14,268,000)		$ (14,268,000)		(26,135,000)
Amount of debt repurchased				$ 0		$ 0
Debt repurchased amount				$ 0		$ 0
Loss on extinguishment of debt					$ 5,900,000
Conversion of principal not included in computation of diluted EPS (in shares) | shares					59,600
Convertible Senior Notes | 2018 Notes
Convertible Senior Notes
Coupon Rate (as a percent)	4.55%
Amount by which if-converted value of the Notes exceed principal amount					$ 16,400,000
Debt repurchased amount	$ 230,000,000
Amount paid for debt repurchased	250,700,000
Portion of repurchase price attributable to equity component recognized as a reduction of additional paid-in-capital					18,100,000
Convertible Senior Notes | 2019 Notes
Convertible Senior Notes
Amount by which if-converted value of the Notes exceed principal amount					34,600,000
Convertible Senior Notes | 2023 Notes
Convertible Senior Notes
Amount issued	250,000,000
Gross proceeds	$ 247,500,000
Coupon Rate (as a percent)	4.375%
Carrying amount of debt components	$ 243,700,000
Carrying amount of conversion option equity components recorded in additional paid-in capital	$ 3,800,000
Senior Notes
Convertible Senior Notes
Unamortized discount			$ (8,420,000)		$ (8,420,000)		$ (9,728,000)