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Shareholders' equity - Additional Information 2 (Detail) (USD $) In Thousands, except Share data, unless otherwise specified | 12 Months Ended |  | 12 Months Ended |  | 0 Months Ended | 12 Months Ended |  | 12 Months Ended | 0 Months Ended | 1 Months Ended |  | 12 Months Ended |  |  |  | 12 Months Ended |  | 12 Months Ended
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Dec. 31, 2013 | Dec. 31, 2012 | Jun. 14, 2013 | Dec. 31, 2013 Consolidated Subsidiaries [Member] | Dec. 31, 2013 2012 Equity Incentive Plan [Member] | Dec. 31, 2012 2012 Equity Incentive Plan [Member] | Dec. 31, 2012 3.5% Convertible Perpetual Preferred Units [Member] Operating Partnership [Member] | Jun. 14, 2013 3.5% Convertible Perpetual Preferred Units [Member] Operating Partnership [Member] | Jun. 14, 2013 Class A Common Shares [Member] | Dec. 31, 2013 Class A Common Shares [Member] | Dec. 31, 2012 Class A Common Shares [Member] | Dec. 31, 2013 Class A Common Shares [Member] 2012 Equity Incentive Plan [Member] | Dec. 31, 2012 Class A Common Shares [Member] 2012 Equity Incentive Plan [Member] | Dec. 31, 2013 Class A Common Shares [Member] Equity Option [Member] 2012 Equity Incentive Plan [Member] | Dec. 31, 2012 Class A Common Shares [Member] Equity Option [Member] 2012 Equity Incentive Plan [Member] | Dec. 31, 2013 Class A Common Shares [Member] Equity Option [Member] 2012 Equity Incentive Plan [Member] Board of Trustees [Member] | Dec. 31, 2013 Class A Common Shares [Member] Subscription Agreement [Member] | Dec. 31, 2012 Class A Common Shares [Member] Subscription Agreement [Member] Option One [Member] | Jun. 14, 2013 Class A Common Shares [Member] Operating Partnership [Member] | Feb. 28, 2014 Class A Common Shares [Member] Subsequent Events [Member] | Feb. 28, 2014 Class A Common Shares [Member] Subsequent Events [Member] 2012 Equity Incentive Plan [Member] | Apr. 30, 2013 Class A Common Shares [Member] Maximum [Member] 2012 Equity Incentive Plan [Member] | Apr. 30, 2013 Class A Common Shares [Member] Minimum [Member] 2012 Equity Incentive Plan [Member] | Dec. 31, 2013 Class A Units [Member] | Dec. 31, 2012 Class A Units [Member] | Dec. 31, 2013 Class A Units [Member] Operating Partnership [Member] | Dec. 31, 2012 Class A Units [Member] Operating Partnership [Member] | Dec. 31, 2013 Series C Convertible Units [Member] | Dec. 31, 2013 Series C Convertible Units [Member] Operating Partnership [Member] | Dec. 31, 2013 Series D Convertible Units [Member] Operating Partnership [Member] | Dec. 31, 2013 Preferred Units [Member]
Class of Stock [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Preferred units issued |  |  | 653,492 |  |  |  | 653,492 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Rate of Preferred units |  |  |  |  |  |  | 3.50% |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Annual distribution |  |  |  |  |  |  | $ 0.525 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Preferred units outstanding |  |  |  |  |  |  |  | 653,492 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Percentage of interest held |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 6.90% | 0.10% |  |  |  |  |  |
Units outstanding |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 199,291,586 | 38,697,333 |  | 31,085,974 | 4,375,000 |
Preferred Units converted into Class A units |  |  |  |  |  |  |  |  | 653,492 |  |  |  |  |  |  |  |  |  | 653,492 |  |  |  |  |  |  |  |  |  |  |  |
Noncontrolling interest | $ 13,245 |  |  | $ 58,000 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | $ 1,760,000 |  |  |  | $ 14,906,000 |  |  | $ 157,000
Issuance of common shares |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 434,783 | 3,333,334 |  |  |  |  |  |  |  |  |  |  |  |  |
Aggregate purchase price of shares |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 50,000 |  |  |  |  |  |  |  |  |  |  |  |  |
Purchase price per share |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | $ 17.25 | $ 15.00 |  |  |  |  |  |  |  |  |  |  |  |  |
Issuance of shares under the plan |  |  |  |  |  |  |  |  |  |  | 650,000 |  | 1,500,000 |  |  |  |  |  |  |  |  | 6,000,000 | 1,500,000 |  |  |  |  |  |  |  |
Plan termination date |  |  |  |  | November 2022 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Stock options granted |  |  |  |  |  | 50,000 |  |  |  | 485,000 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Vesting period |  |  |  |  |  | 4 years |  |  |  |  |  | 4 years | 4 years |  |  |  |  |  |  |  | 4 years |  |  |  |  |  |  |  |  |  |
Expiration period of options |  |  |  |  |  | 10 years |  |  |  |  |  | 10 years | 10 years |  |  |  |  |  |  |  | 10 years |  |  |  |  |  |  |  |  |  |
Issuance of shares under the plan | 550,000 | 700,000 |  |  |  |  |  |  |  | 550,000 |  | 485,000 |  |  |  |  |  |  |  | 940,000 |  |  |  |  |  |  |  |  |  |  |
Stock options cancelled | 60,000 |  |  |  |  |  |  |  |  |  |  | 60,000 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Stock Options, Exercised |  |  |  |  |  |  |  |  |  |  |  | 0 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Restricted stock units |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 92,000 |  |  |  |  |  |  |  |  |  |
Share-based compensation expense | $ 1,079 | $ 70 |  |  |  |  |  |  |  |  |  |  |  | $ 762 | $ 70 | $ 317 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Common stock issued |  |  |  |  |  |  |  |  |  |  |  | 19,500 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |

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- Definition Period from grant date that an equity-based award expires, 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 (a)(2) -URI http://asc.fasb.org/extlink&oid=6415400&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=6415400&loc=d3e5070-113901 + Details
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- Definition Number of shares (or other type of equity) issued during the period as a result of any equity-based compensation plan other than an employee stock ownership plan (ESOP), net of any shares forfeited. Shares issued could result from the issuance of restricted stock, the exercise of stock options, stock issued under employee stock purchase plans, and/or other employee benefit plans. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Regulation S-X (SX) -Number 210 -Section 04 -Article 3 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 505 -SubTopic 10 -Section 50 -Paragraph 2 -URI http://asc.fasb.org/extlink&oid=6928386&loc=d3e21463-112644 Reference 3: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 505 -SubTopic 10 -Section S99 -Paragraph 1 -Subparagraph (SX 210.3-04) -URI http://asc.fasb.org/extlink&oid=27012166&loc=d3e187085-122770 Reference 4: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Regulation S-X (SX) -Number 210 -Section 02 -Paragraph 29, 30 -Article 5 + Details
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