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Contract Assets and Liabilities - Summary of Assets and Liabilities (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Contractors [Line Items]
Contract assets	$ 185,803	$ 217,109
Contract liabilities	(158,396)	(105,486)
Net contract assets (liabilities)	27,407	111,623
Changes in contract assets	(31,360)	$ 16,443	$ 28,141
Net Period Change
Contractors [Line Items]
Changes in contract assets	(31,306)
Changes in contract liabilities	(52,910)
Changes in net contract assets (liabilities)	$ (84,216)

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The amount of increase(decrease)in net contract assets(liabilities) during the year.

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Amount, after allowance for credit loss, of right to consideration in exchange for good or service transferred to customer when right is conditioned on something other than passage of time, classified as current.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
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Amount of obligation to transfer good or service to customer for which consideration has been received or is receivable, classified as current.

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Amount of increase (decrease) in right to consideration in exchange for good or service transferred to customer when right is conditioned on something other than passage of time.

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The change during the period, either increase or decrease, in amounts payable to customers. The term customers generally excludes other broker-dealers; persons who are principal officers, directors, and stockholders; and persons whose securities or funds are part of the regulatory net capital of the broker-dealer. Another broker-dealer's account can be classified as a customer if the account is carried as an omnibus account in compliance with certain regulations. The accounts of principal officers, directors and stockholders may be combined in the customer captions if they are not material and the combination is disclosed in the oath that is required to accompany the annual audited FOCUS Report.

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