Other Non-Current Liabilities - Summary of Other Non-Current Liabilities (Details) - USD ($) $ in Thousands	Jun. 30, 2019	Dec. 31, 2018
Liabilities, Noncurrent [Abstract]
Derivative instruments	$ 1,140	$ 3,075
Unrecognized tax benefits	804	804
Deferred rent	0	7,834
Retirement benefits	4,002	3,616
Deferred transition revenue	2,472	945
Others	676	247
Other non-current liabilities	$ 9,094	$ 16,521

Amount of obligation to transfer good or service to customer for which consideration has been received or is receivable, classified as noncurrent.

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For a classified balance sheet, the cumulative difference between the rental income or 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, by the lessor or lessee, respectively, more than one year after the balance sheet date.

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Fair value of liability arising from contracts that meet the criteria of being accounted for as derivative instruments, financial instrument or contract used to mitigate a specified risk (hedge), energy marketing activities (trading activities), expected to be settled after one year or beyond the normal operating cycle, if longer. Examples of energy marketing activities include, but are not limited to, trading of electricity, coal, natural gas and oil using financial instruments, including, but not limited to, forward contracts, options and swaps.

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Aggregated carrying amounts of obligations as of the balance sheet date, excluding long-term debt, incurred as part of the normal operations that are expected to be paid after one year or beyond the normal operating cycle, if longer. Alternate captions include Total Deferred Credits and Other Liabilities.

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Amount recognized for uncertainty in income taxes classified as noncurrent.

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Amount of liabilities classified as other, due after one year or the normal operating cycle, if longer.

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Amount of liability, recognized in statement of financial position, for defined benefit pension and other postretirement plans, classified as noncurrent.

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