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The cumulative difference between the rental payments required by a lease agreement and the rental income or expense recognized on a straight-line basis, or other systematic and rational basis more representative of the time pattern in which use or benefit is granted or derived from the leased property, expected to be recognized in income or expense over the term of the leased property by the lessor or lessee, respectively.

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Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 840
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No definition available.

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Amount of operating lease income from lease payments and variable lease payments paid and payable to lessor. Includes, but is not limited to, variable lease payments not included in measurement of lease receivable.

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Present value of lessee's discounted obligation for lease payments from operating lease.

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-Publisher FASB
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Amount of lessee's right to use underlying asset under operating lease.

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Amount, including tax collected from customer, of revenue from satisfaction of performance obligation by transferring promised good or service to customer. Tax collected from customer is tax assessed by governmental authority that is both imposed on and concurrent with specific revenue-producing transaction, including, but not limited to, sales, use, value-added and excise.

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Summary of Significant Accounting Policies (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017	Dec. 31, 2017
Balance sheet impact
Operating lease right-of-use assets	$ 88,781		$ 92,984
Operating lease liabilities	97,308		102,912
Income statement impact
Rental revenue	71,033	$ 64,251
ASU 2016-02
Balance sheet impact
Operating lease right-of-use assets			92,984
Operating lease liabilities			102,912
As Previously Reported \| ASU 2016-02
Balance sheet impact
Deferred rent payable			9,928
Currently Reported \| Proposed ASU
Income statement impact
Rental revenue	71,033	64,251
Adjustment \| ASU 2016-02
Balance sheet impact
Operating lease right-of-use assets			92,984
Operating lease liabilities			102,912
Deferred rent payable			$ (9,928)
Adjustment \| Proposed ASU
Income statement impact
Rental revenue	(71,033)	(64,251)
Power Revenue
Income statement impact
Revenue	36,403	30,861
Power Revenue \| Currently Reported \| Proposed ASU
Income statement impact
Revenue	36,403	30,861
Power Revenue \| Adjustment \| Proposed ASU
Income statement impact
Revenue	(36,403)	(30,861)
Tenant Reimbursement And Other Revenue
Income statement impact
Revenue	2,572	2,276
Tenant Reimbursement And Other Revenue \| Currently Reported \| Proposed ASU
Income statement impact
Revenue	2,572	2,276
Tenant Reimbursement And Other Revenue \| Adjustment \| Proposed ASU
Income statement impact
Revenue	(2,572)	(2,276)
Rental Power And Related Revenue \| Adjustment \| Proposed ASU
Income statement impact
Revenue	110,008	97,388
Rental Power And Related Revenue \| Pro Forma \| Proposed ASU
Income statement impact
Revenue	$ 110,008	$ 97,388