Represents the percentage of debt discount that was originally recognized at the issuance of the instrument.

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The principal amount of notes used as denominator for purposes of computing the conversion ratio of convertible debt.

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Debt Issuance Cost Amortization Period

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Percentage of Underwriting Fee

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Represents the percentage of principal amount used in computation of the redemption price to be paid on conversion of convertible notes at the request of the debt holders and upon the occurrence of a designated event.

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Represents the number of days of written notice to be made to the holders of the notes required for redemption.

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The value of the financial instrument(s) that the original debt is being converted into in a noncash (or part noncash) transaction. "Part noncash" refers to that portion of the transaction not resulting in cash receipts or cash payments in the period.

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The number of shares issued in exchange for the original debt being converted in a noncash (or part noncash) transaction. "Part noncash" refers to that portion of the transaction not resulting in cash receipts or payments in the period.

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Ratio applied to the conversion of debt instrument into equity with equity shares divided by debt principal amount.

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Threshold period of specified consecutive trading days within which common stock price to conversion price of convertible debt instrument must exceed threshold percentage for specified number of trading days to trigger conversion feature.

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Minimum percentage of common stock price to conversion price of convertible debt instruments to determine eligibility of conversion.

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Threshold number of specified trading days that common stock price to conversion price of convertible debt instruments must exceed threshold percentage within a specified consecutive trading period to trigger conversion feature.

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Face (par) amount of debt instrument at time of issuance.

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Effective interest rate for the funds borrowed under the debt agreement considering interest compounding and original issue discount or premium.

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Contractual interest rate for funds borrowed, under the debt agreement.

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Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

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Percentage price of original principal amount of debt at which debt can be redeemed by the issuer.

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Fair value amount of debt instrument that was repurchased.

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Face (par) amount of the original debt instrument that was repurchased.

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Period of time between issuance and maturity of debt instrument, in PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

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Amount, after accumulated amortization, of debt discount.

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Amount, after accumulated amortization, of debt issuance costs. Includes, but is not limited to, legal, accounting, underwriting, printing, and registration costs.

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Exchangeable Senior Notes - Additional Information (Details)		1 Months Ended			12 Months Ended
	Jun. 21, 2013 USD ($)	Apr. 30, 2016 USD ($) shares	Feb. 29, 2016 USD ($) shares	Sep. 30, 2015 USD ($)	Dec. 31, 2017 USD ($) d	Jan. 01, 2018 USD ($)	Oct. 31, 2017 USD ($)	Aug. 31, 2017 USD ($)	Dec. 31, 2016 USD ($)	Dec. 31, 2015 USD ($)	Sep. 15, 2015 USD ($)
Common Stock
Debt Instrument [Line Items]
Converted instrument, shares issued (in shares) \| shares		18,031	130,909
Converted instrument, amount		$ 1,686,000	$ 11,380,000
2013 Notes
Debt Instrument [Line Items]
Notes exchange, threshold percentage					130.00%
Notes exchange, threshold trading days \| d					20
Notes exchange, threshold consecutive trading days \| d					30
Effective rate of interest					4.00%
Operating Partnership
Debt Instrument [Line Items]
Related debt issuance costs					$ 6,620,000				$ 9,033,000
Operating Partnership \| 2015 Notes
Debt Instrument [Line Items]
Principal amount of notes issued				$ 575,000,000
Fixed Rate				3.125%	3.125%
Related debt issuance costs				$ 11,992,000
Underwriting fee percentage				2.00%
Amortization period				5 years
Conversion ratio, number of shares per $1,000 principal amount, numerator					10.66
Principal amount used for debt instrument conversion ratio					$ 1,000
Redemption price as percentage of principal amount of notes plus accrued and unpaid interest				100.00%
Redemption price as percentage of principal amount of notes at request of debt holders and upon occurrence of designated event				100.00%
Operating Partnership \| 2015 Notes \| Minimum
Debt Instrument [Line Items]
Number of days of written notice to holders of notes required for redemption				30 days
Operating Partnership \| 2015 Notes \| Maximum
Debt Instrument [Line Items]
Number of days of written notice to holders of notes required for redemption				60 days
Operating Partnership \| 2013 Notes
Debt Instrument [Line Items]
Principal amount of notes issued	$ 250,000,000
Fixed Rate	2.375%				2.375%
Related debt issuance costs	$ 1,672,000				$ 35,000				43,000	$ 605,000
Conversion ratio, number of shares per $1,000 principal amount, numerator					18.85
Principal amount used for debt instrument conversion ratio					$ 1,000
Redemption price as percentage of principal amount of notes plus accrued and unpaid interest	100.00%
Redemption price as percentage of principal amount of notes at request of debt holders and upon occurrence of designated event	100.00%
Discount rate (as a percent)	1.50%
Unamortized cash discount	$ 3,750,000				184,000				788,000	6,931,000
Amortization period	5 years
Principal amount repurchased					13,911,000			$ 13,911,000	22,194,000	164,636,000	$ 164,636,000
Total consideration paid for repurchase		$ 2,555,000	$ 19,639,000		$ 20,042,000		$ 20,042,000		$ 35,261,000	$ 227,212,000	$ 227,212,000
Operating Partnership \| 2013 Notes \| Subsequent Event
Debt Instrument [Line Items]
Principal amount repurchased						$ 37,704,000
Total consideration paid for repurchase						$ 58,465,000
Operating Partnership \| 2013 Notes \| Minimum
Debt Instrument [Line Items]
Number of days of written notice to holders of notes required for redemption	30 days
Operating Partnership \| 2013 Notes \| Maximum
Debt Instrument [Line Items]
Number of days of written notice to holders of notes required for redemption	60 days