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Schedule III - Real Estate and Accumulated Depreciation - Change in Balance of Real Estate 2 (Detail) - USD ($) $ in Thousands | 12 Months Ended
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Dec. 31, 2016 | Dec. 31, 2015 | Dec. 31, 2014
SEC Schedule III, Real Estate and Accumulated Depreciation [Line Items] |  |  |
Impairment charge | $ 2,016 | $ 622 | $ 14,238
Roseville, Minnesota [Member] |  |  |
SEC Schedule III, Real Estate and Accumulated Depreciation [Line Items] |  |  |
Impairment charge |  |  | $ 14,200
Real Estate Held for Sale [Member] |  |  |
SEC Schedule III, Real Estate and Accumulated Depreciation [Line Items] |  |  |
Real estate held for sale, gross | $ 11,454 | $ 1,899 |

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- Definition Amount of write-down of assets recognized in the income statement. Includes, but is not limited to, losses from tangible assets, intangible assets and goodwill. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 360 -SubTopic 10 -Section 45 -Paragraph 4 -URI http://asc.fasb.org/extlink&oid=51824106&loc=d3e2420-110228 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 230 -SubTopic 10 -Section 45 -Paragraph 28 -Subparagraph (b) -URI http://asc.fasb.org/extlink&oid=56944662&loc=d3e3602-108585 + Details
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