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Significant Accounting Policies (Tables) | 9 Months Ended
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Sep. 30, 2018
Accounting Policies [Abstract] |
Summary of identified intangible assets (acquired above-market leases and in-place leases) and intangible liabilities (acquired below-market leases) | The following summarizes our identified intangible assets (acquired above-market leases and in-place leases) and intangible liabilities (acquired below-market leases) as of September 30, 2018 and December 31, 2017 (in thousands):
| September 30, 2018 |  | December 31, 2017
Identified intangible assets (included in other assets): |  |  |
Gross amount | $ | 261,216 |  |  | $ | 325,880 |
Accumulated amortization | (239,479 | ) |  | (277,038 | )
Net(1) | $ | 21,737 |  |  | $ | 48,842 |
Identified intangible liabilities (included in deferred revenue): |  |  |
Gross amount | $ | 274,120 |  |  | $ | 540,283 |
Accumulated amortization | (251,895 | ) |  | (402,583 | )
Net(1) | $ | 22,225 |  |  | $ | 137,700 |
(1) | As of September 30, 2018 and December 31, 2017, $0.2 million and $13.9 million, respectively, and $0.0 million and $4.1 million, respectively, of net intangible assets and net intangible liabilities, were reclassified to assets held for sale and liabilities related to assets held for sale.
Schedule of marketable securities | At September 30, 2018 and December 31, 2017, we held the following marketable securities (in thousands):
| September 30, 2018 |  | December 31, 2017
Commercial mortgage-backed securities | $ | 28,538 |  |  | $ | 28,579 |
Total marketable securities available-for-sale | $ | 28,538 |  |  | $ | 28,579 |

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- Definition Tabular disclosure of available-for-sale securities which includes, but is not limited to, changes in the cost basis and fair value, fair value and gross unrealized gain (loss), fair values by type of security, contractual maturity and classification, amortized cost basis, contracts to acquire securities to be accounted for as available-for-sale, debt maturities, transfers to trading, change in net unrealized holding gain (loss) net of tax, continuous unrealized loss position fair value, aggregate losses qualitative disclosures, other than temporary impairment (OTTI) losses or other disclosures related to available for sale securities. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 942 -SubTopic 320 -Section 50 -Paragraph 2 -URI http://asc.fasb.org/extlink&oid=75019621&loc=d3e62557-112803 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 320 -SubTopic 10 -Section 50 -Paragraph 7 -URI http://asc.fasb.org/extlink&oid=82897076&loc=d3e27337-111563 Reference 3: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 320 -SubTopic 10 -Section 50 -Paragraph 3 -URI http://asc.fasb.org/extlink&oid=82897076&loc=d3e27198-111563 Reference 4: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 942 -SubTopic 320 -Section 50 -Paragraph 3 -URI http://asc.fasb.org/extlink&oid=75019621&loc=d3e62586-112803 Reference 5: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 320 -SubTopic 10 -Section 50 -Paragraph 2 -URI http://asc.fasb.org/extlink&oid=82897076&loc=d3e27161-111563 Reference 6: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 320 -SubTopic 10 -Section 50 -Paragraph 9 -URI http://asc.fasb.org/extlink&oid=82897076&loc=d3e27357-111563 Reference 7: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 320 -SubTopic 10 -Section 50 -Paragraph 6 -URI http://asc.fasb.org/extlink&oid=82897076&loc=d3e27290-111563 + Details
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