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Share-based Compensation - Additional Information (Details) $ / shares in Units, fungible_unit in Millions | 1 Months Ended | 3 Months Ended | 9 Months Ended | 12 Months Ended |  |
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Aug. 31, 2014 shares | Sep. 30, 2018 USD ($) unit / shares unit fungible_unit shares | Sep. 30, 2017 USD ($) | Sep. 30, 2018 USD ($) unit / shares unit fungible_unit $ / shares shares | Sep. 30, 2017 USD ($) shares | Dec. 31, 2017 USD ($) shares | Dec. 31, 2016 shares | Jan. 01, 2008 shares
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |  |  |  |  |  |  |
Capitalized to assets associated with compensation expense related to our long-term compensation plans, restricted stock and stock options |  | $ 1,600,000 | $ 1,400,000 | $ 4,700,000 | $ 5,000,000 |  |  |
Stock options |  |  |  |  |  |  |  |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |  |  |  |  |  |  |
Period of commencement of option vesting, from date of grant (in years) |  |  |  | 1 year |  |  |  |
Exercise price of options granted, low end of the range (in dollars per share) | $ / shares |  |  |  | $ 20.67 |  |  |  |
Exercise price of options granted, high end of the range (in dollars per share) | $ / shares |  |  |  | $ 137.18 |  |  |  |
Remaining weighted average contractual life of the options outstanding (in years) |  |  |  | 3 years 4 months |  |  |  |
Remaining average contractual life of the options exercisable (in years) |  |  |  | 3 years 4 months |  |  |  |
Total unrecognized compensation cost related to unvested stock awards |  | $ 3,700,000 |  | $ 3,700,000 |  |  |  |
Weighted average period for recognition of compensation cost related to unvested stock awards (in years) |  |  |  | 1 year |  |  |  |
Weighted average fair value of options granted during the period |  |  |  | $ 84,068 |  | $ 3,816,652 |  |
Stock options | Minimum |  |  |  |  |  |  |  |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |  |  |  |  |  |  |
Award expiration period (in years) |  |  |  | 5 years |  |  |  |
Options vesting period (in years) |  |  |  | 1 year |  |  |  |
Stock options | Maximum |  |  |  |  |  |  |  |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |  |  |  |  |  |  |
Award expiration period (in years) |  |  |  | 10 years |  |  |  |
Options vesting period (in years) |  |  |  | 5 years |  |  |  |
Class O LTIP Units |  |  |  |  |  |  |  |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |  |  |  |  |  |  |
Share Based Compensation Arrangement by Share Based Payment Award, Preferred Unit Distributions as a Percentage of Common Unit Distributions |  | 10.00% |  | 10.00% |  |  |  |
Restricted Stock Awards |  |  |  |  |  |  |  |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |  |  |  |  |  |  |
Compensation expense |  |  |  | $ 9,441,158 | 9,809,749 |  |  |
Total unrecognized compensation cost related to unvested stock awards |  | $ 13,400,000 |  | $ 13,400,000 |  |  |  |
Weighted average period for recognition of compensation cost related to unvested stock awards (in years) |  |  |  | 1 year 10 months |  |  |  |
Annual award vesting rate, low end of range (as a percent) |  |  |  | 15.00% |  |  |  |
Annual award vesting rate, high end of range (as a percent) |  |  |  | 35.00% |  |  |  |
Fair value of restricted stock vested during the period |  |  |  | $ 9,800,000 |  | $ 9,400,000 |  |
Weighted average fair value of options granted during the period |  |  |  | $ 1,222,031 | $ 9,905,986 |  |  |
Awards granted (in shares) | shares |  |  |  | 11,700 | 96,185 |  |  |
Awards outstanding (in shares) | shares |  | 3,300,816 |  | 3,300,816 |  | 3,298,216 | 3,202,031 |
LTIP units |  |  |  |  |  |  |  |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |  |  |  |  |  |  |
Weighted average fair value of options granted during the period |  |  |  | $ 20,600,000 |  | $ 20,500,000 |  |
Performance Shares |  |  |  |  |  |  |  |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |  |  |  |  |  |  |
Total unrecognized compensation cost related to unvested stock awards |  | $ 5,200,000 |  | $ 5,200,000 |  |  |  |
Weighted average period for recognition of compensation cost related to unvested stock awards (in years) |  |  |  | 1 year |  |  |  |
Share-based compensation |  | $ 2,300,000 | 2,500,000 | $ 11,400,000 | $ 15,100,000 |  |  |
Third Amendment and Restated 2005 Stock Option and Incentive Plan |  |  |  |  |  |  |  |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |  |  |  |  |  |  |
Maximum fungible units that may be granted (in shares) | unit |  | 27,030,000 |  | 27,030,000 |  |  |  |
Fungible units per share (in fungible units per share) | unit / shares |  | 3.74 |  | 3.74 |  |  |  |
Shares that may be issued if equal to fungible units (shares) (less than) | shares |  | 27,030,000 |  | 27,030,000 |  |  |  |
Fungible units | fungible_unit |  | 7.3 |  | 7.3 |  |  |  |
Third Amendment and Restated 2005 Stock Option and Incentive Plan | Stock options |  |  |  |  |  |  |  |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |  |  |  |  |  |  |
Compensation expense |  | $ 1,100,000 | 2,000,000 | $ 4,300,000 | 5,900,000 |  |  |
Stock options, stock appreciation rights and other awards |  |  |  |  |  |  |  |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |  |  |  |  |  |  |
Fungible units per share (in fungible units per share) | unit / shares |  | 0.73 |  | 0.73 |  |  |  |
Award expiration period (in years) |  |  |  | 5 years |  |  |  |
All other awards |  |  |  |  |  |  |  |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |  |  |  |  |  |  |
Fungible units per share (in fungible units per share) | unit / shares |  | 1.0 |  | 1.0 |  |  |  |
Award expiration period (in years) |  |  |  | 10 years |  |  |  |
2014 Outperformance Plan |  |  |  |  |  |  |  |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |  |  |  |  |  |  |
Compensation expense |  | $ 0 | 1,900,000 | $ 0 | 8,200,000 |  |  |
Capitalized to assets associated with compensation expense related to our long-term compensation plans, restricted stock and stock options |  |  |  | 27,900,000 |  |  |  |
LTIP units earned (in shares) | shares | 610,000 |  |  |  |  |  |  |
Award period (in years) | 3 years |  |  |  |  |  |  |
Maximum award to be earned, if performance reaches maximum threshold, first performance period | 0.333 |  |  |  |  |  |  |
Maximum award to be earned, if performance reaches maximum threshold, second performance period | 0.667 |  |  |  |  |  |  |
2014 Outperformance Plan | Vesting on August 31, 2017 |  |  |  |  |  |  |  |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |  |  |  |  |  |  |
Percentage of units vested | 50.00% |  |  |  |  |  |  |
2014 Outperformance Plan | Vesting on August 31, 2018 |  |  |  |  |  |  |  |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |  |  |  |  |  |  |
Percentage of units vested | 50.00% |  |  |  |  |  |  |
Deferred Stock Compensation Plan for Directors |  |  |  |  |  |  |  |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |  |  |  |  |  |  |
Compensation expense |  | $ 100,000 | $ 100,000 | $ 2,200,000 | $ 2,200,000 |  |  |
Maximum percentage of the annual retainer fee, chairman fees and meeting fees that may be deferred by non-employee directors (percent) |  | 100.00% |  | 100.00% |  |  |  |
Awards granted (in shares) | shares |  |  |  | 12,541 |  |  |  |
Shares issued (in shares) | shares |  |  |  | 9,394 |  |  |  |
Awards outstanding (in shares) | shares |  | 112,394 |  | 112,394 |  |  |  |
Employee Stock Purchase Plan |  |  |  |  |  |  |  |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |  |  |  |  |  |  |
Shares of common stock available for issuance (shares) | shares |  |  |  |  |  |  |  | 500,000
Duration of each offering period starting the first day of each calendar quarter (in months) |  |  |  | 3 months |  |  |  |
Discount from market price |  |  |  | 85.00% |  |  |  |
Shares of common stock issued (shares) | shares |  | 112,815 |  | 112,815 |  |  |  |

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- Definition Represents the number of shares that would be issued under the plan if shares issued is equal to fungible units; actual shares issued may be more or less depending on the type of awards issued and the ratio of fungible units to shares under each award. + References No definition available. + Details
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- Definition Represents the expense recognized during the period arising from equity-based compensation arrangements (for example, shares of stock, unit, stock options or other equity instruments) with employees, directors and certain consultants qualifying for treatment as employees. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 718 -SubTopic 10 -Section S99 -Paragraph 1 -Subparagraph (SAB Topic 14.F) -URI http://asc.fasb.org/extlink&oid=27013229&loc=d3e301413-122809 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 718 -SubTopic 10 -Section 50 -Paragraph 1 -Subparagraph (b) -URI http://asc.fasb.org/extlink&oid=96867065&loc=d3e5047-113901 Reference 3: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 718 -SubTopic 10 -Section 50 -Paragraph 2 -Subparagraph (h)(1)(i) -URI http://asc.fasb.org/extlink&oid=96867065&loc=d3e5070-113901 + Details
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- Definition Represents the compensation cost capitalized during the period arising from equity-based compensation arrangements (for example, shares of stock, units, stock options or other equity instruments) with employees, directors and certain consultants qualifying for treatment as employees. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 718 -SubTopic 10 -Section 50 -Paragraph 2 -Subparagraph (h)(1)(ii) -URI http://asc.fasb.org/extlink&oid=96867065&loc=d3e5070-113901 + Details
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- Definition Unrecognized cost of unvested share-based compensation awards. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 718 -SubTopic 10 -Section 50 -Paragraph 2 -Subparagraph (i) -URI http://asc.fasb.org/extlink&oid=96867065&loc=d3e5070-113901 + Details
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- Definition Weighted average period over which unrecognized compensation is expected to be recognized for equity-based compensation plans, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 718 -SubTopic 10 -Section 50 -Paragraph 2 -Subparagraph (i) -URI http://asc.fasb.org/extlink&oid=96867065&loc=d3e5070-113901 + Details
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- Definition The aggregate amount of noncash, equity-based employee remuneration. This may include the value of stock or unit options, amortization of restricted stock or units, and adjustment for officers' compensation. As noncash, this element is an add back when calculating net cash generated by operating activities using the indirect method. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 230 -SubTopic 10 -Section 45 -Paragraph 28 -Subparagraph (a) -URI http://asc.fasb.org/extlink&oid=98514028&loc=d3e3602-108585 + Details
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- Definition Discount rate from fair value on offering date that participants pay for shares. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 718 -SubTopic 10 -Section 50 -Paragraph 2 -URI http://asc.fasb.org/extlink&oid=96867065&loc=d3e5070-113901 + Details
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- Definition The number of grants made during the period on other than stock (or unit) option plans (for example, phantom stock or unit plan, stock or unit appreciation rights plan, performance target plan). + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 718 -SubTopic 10 -Section 50 -Paragraph 2 -Subparagraph (c)(2)(iii)(1) -URI http://asc.fasb.org/extlink&oid=96867065&loc=d3e5070-113901 + Details
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- Definition The number of non-vested equity-based payment instruments, excluding stock (or unit) options, that validly exist and are outstanding as of the balance sheet date. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 718 -SubTopic 10 -Section 50 -Paragraph 2 -Subparagraph (c)(2)(i)-(ii) -URI http://asc.fasb.org/extlink&oid=96867065&loc=d3e5070-113901 + Details
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- Definition Fair value of share-based awards for which the grantee gained the right by satisfying service and performance requirements, to receive or retain shares or units, other instruments, or cash. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 718 -SubTopic 10 -Section 50 -Paragraph 2 -Subparagraph (d)(2) -URI http://asc.fasb.org/extlink&oid=96867065&loc=d3e5070-113901 + Details
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- Definition The difference between the maximum number of shares (or other type of equity) authorized for issuance under the plan (including the effects of amendments and adjustments), and the sum of: 1) the number of shares (or other type of equity) already issued upon exercise of options or other equity-based awards under the plan; and 2) shares (or other type of equity) reserved for issuance on granting of outstanding awards, net of cancellations and forfeitures, if applicable. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 718 -SubTopic 10 -Section 50 -Paragraph 2 -URI http://asc.fasb.org/extlink&oid=96867065&loc=d3e5070-113901 + Details
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- Definition The floor of a customized range of exercise prices for purposes of disclosing shares potentially issuable under outstanding stock option awards on all stock option plans and other required information pertaining to awards in the customized range. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 718 -SubTopic 10 -Section 50 -Paragraph 2 -Subparagraph (g) -URI http://asc.fasb.org/extlink&oid=96867065&loc=d3e5070-113901 + Details
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- Definition The ceiling of a customized range of exercise prices for purposes of disclosing shares potentially issuable under outstanding stock option awards on all stock option plans and other required information pertaining to awards in the customized range. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 718 -SubTopic 10 -Section 50 -Paragraph 2 -Subparagraph (g) -URI http://asc.fasb.org/extlink&oid=96867065&loc=d3e5070-113901 + Details
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- Definition Percentage of vesting of share-based compensation awards. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 718 -SubTopic 10 -Section 50 -Paragraph 2 -Subparagraph (a)(1) -URI http://asc.fasb.org/extlink&oid=96867065&loc=d3e5070-113901 + Details
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