Real Estate Charges (Details) $ in Thousands, ft² in Millions	9 Months Ended	12 Months Ended
Sep. 30, 2018 USD ($) ft²	Dec. 31, 2017 USD ($)
Restructuring and Related Activities [Abstract]
Square feet of office space sub-leased (over) \| ft²	1
Real estate liability restructuring reserve [Abstract]
Balance as of beginning of period	$ 113,635	$ 112,932
Expense incurred	6,490	28,507
Deferred rent	0	7,083
Payments made	(32,868)	(39,122)
Interest accretion	3,284	4,235
Balance as of end of period	$ 90,541	$ 113,635

Amount recognized for the passage of time, typically for liabilities, that have been discounted to their net present values. Excludes accretion associated with asset retirement obligations.

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Area of a real estate property.

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Amount of cash payments made as the result of exit or disposal activities. Excludes payments associated with a discontinued operation or an asset retirement obligation.

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Amount of expenses associated with exit or disposal activities pursuant to an authorized plan. Excludes expenses related to a discontinued operation or an asset retirement obligation.

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Carrying amount (including both current and noncurrent portions of the accrual) as of the balance sheet date pertaining to a specified type of cost associated with exit from or disposal of business activities or restructuring pursuant to a duly authorized plan.

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Amount of expense (reversal of expense) which increases (decreases) the restructuring reserve from an adjustment to a previously accrued restructuring liability.

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