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Investments in Unconsolidated Joint Ventures (Statements of Operations of the Joint Ventures) (Details) - USD ($) $ in Thousands | 3 Months Ended | 12 Months Ended
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Dec. 31, 2017 | Sep. 30, 2017 | Jun. 30, 2017 | Mar. 31, 2017 | Dec. 31, 2016 | Sep. 30, 2016 | Jun. 30, 2016 | Mar. 31, 2016 | Dec. 31, 2017 | Dec. 31, 2016 | Dec. 31, 2015
Schedule of Equity Method Investments [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Total revenue |  | $ 655,229 | $ 657,712 | $ 656,907 | $ 632,228 | $ 636,061 | $ 625,228 | $ 623,546 | $ 665,985 | $ 2,602,076 |  | $ 2,550,820 |  | $ 2,490,821 |
Expenses |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Depreciation and amortization |  |  |  |  |  |  |  |  |  | 617,547 |  | 694,403 |  | 639,542 |
Total expenses |  |  |  |  |  |  |  |  |  | 1,693,966 |  | 1,725,036 |  | 1,641,456 |
Operating income |  |  |  |  |  |  |  |  |  | 908,110 |  | 825,784 |  | 849,365 |
Other income (expense) |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Interest expense |  |  |  |  |  |  |  |  |  | (374,481) |  | (412,849) |  | (432,196) |
Net income |  |  |  |  |  |  |  |  |  | 562,481 |  | 569,977 |  | 799,918 |
Income from unconsolidated joint ventures |  |  |  |  |  |  |  |  |  | 11,232 |  | 8,074 |  | 22,770 |
Gain on sale of investment in unconsolidated joint venture |  |  |  |  |  |  |  |  |  | 0 |  | 59,370 |  | 0 |
Straight-line rent adjustments |  |  |  |  |  |  |  |  |  | 54,800 |  | 31,700 |  | 80,000 |
Mortgage and notes payable, net |  | 2,979,281 |  |  |  | 2,063,087 |  |  |  | 2,979,281 |  | 2,063,087 |  |  |
Above and below market rent adjustments, net |  |  |  |  |  |  |  |  |  | 23,500 |  | 30,200 |  | 35,900 |
Gain on sale of investment in unconsolidated joint venture |  |  |  |  |  |  |  |  |  | 0 |  | 55,707 |  | 0 |
Unconsolidated Joint Ventures [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Schedule of Equity Method Investments [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Total revenue | [1] |  |  |  |  |  |  |  |  | 222,517 |  | 177,182 |  | 155,642 |
Expenses |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Operating |  |  |  |  |  |  |  |  |  | 90,542 |  | 76,741 |  | 65,093 |
Depreciation and amortization |  |  |  |  |  |  |  |  |  | 57,079 |  | 44,989 |  | 36,057 |
Total expenses |  |  |  |  |  |  |  |  |  | 147,621 |  | 121,730 |  | 101,150 |
Operating income |  |  |  |  |  |  |  |  |  | 74,896 |  | 55,452 |  | 54,492 |
Other income (expense) |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Interest expense |  |  |  |  |  |  |  |  |  | (46,371) |  | (34,016) |  | (32,176) |
Net income |  |  |  |  |  |  |  |  |  | 28,525 |  | 21,436 |  | 22,316 |
Company's share of net income |  |  |  |  |  |  |  |  |  | 18,439 |  | 9,873 |  | 22,031 | [2]
Basis differential |  |  |  |  |  |  |  |  |  | (7,207) | [3] | (1,799) | [3] | 739 |
Income from unconsolidated joint ventures |  |  |  |  |  |  |  |  |  | 11,232 |  | 8,074 |  | 22,770 |
Straight-line rent adjustments |  |  |  |  |  |  |  |  |  | 21,700 |  | 18,100 |  | 3,900 |
Mortgage and notes payable, net |  | $ 1,437,440 |  |  |  | $ 865,665 |  |  |  | 1,437,440 |  | 865,665 |  |  |
BP/CRF 901 New York Avenue LLC [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Other income (expense) |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Mortgage and notes payable, net |  |  |  |  |  |  |  |  |  |  |  |  |  | 225,000 |
Gain on sale of investment in unconsolidated joint venture |  |  |  |  |  |  |  |  |  |  |  |  |  | $ 24,500 |
Colorado Center [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Other income (expense) |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Straight-line rent adjustments |  |  |  |  |  |  |  |  |  | 1,900 |  | 1,400 |  |  |
Above and below market rent adjustments, net |  |  |  |  |  |  |  |  |  | $ 2,900 |  | $ 900 |  |  |
[1] | Includes straight-line rent adjustments of approximately $21.7 million, $18.1 million and $3.9 million for the years ended December 31, 2017, 2016 and 2015, respectively.
[2] | During the year ended December 31, 2015, the Company received a distribution of approximately $24.5 million, which was generated from the excess loan proceeds from the refinancing of 901 New York Avenue’s mortgage loan to a new 10-year mortgage loan totaling $225.0 million. The Company’s allocation of income and distributions for the year ended December 31, 2015 was not proportionate to its nominal ownership interest as a result of the achievement of specified investment return thresholds, as provided for in the joint venture agreement.
[3] | Includes straight-line rent adjustments of approximately $1.9 million and $1.4 million for the years ended December 31, 2017 and 2016, respectively. Also includes net above-/below-market rent adjustments of approximately $2.9 million and $0.9 million for the years ended December 31, 2017 and 2016, respectively.

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