Revenue (Tables)

9 Months Ended

Sep. 30, 2019

Revenue from Contract with Customer [Abstract]

Contract with Customer, Asset and Liability

The following table presents the beginning and ending balances of costs in excess of billings, billings in excess of cost and unearned revenue as of September 30, 2019 and December 31, 2018, respectively, and revenue recognized during the nine months ended September 30, 2019 and 2018, respectively, that was in billings in excess of cost and unearned revenue at the beginning of the period (in thousands):

	September 30, 2019			December 31, 2018
Costs in excess of billings	$	24,951		$	22,634
Billings in excess of cost	(38,672		)	(17,857		)
Unearned revenue	(21,860		)	(12,028		)

The increase in contract liabilities as of September 30, 2019 compared with December 31, 2018 was primarily driven by the seasonality in our businesses.

	Nine Months Ended September 30, 2019		Nine Months Ended September 30, 2018
Revenue recognized in the period from:
Amounts included in billings in excess of cost  at the beginning of the period	$	14,137	$	9,294
Amounts included in unearned revenue  at the beginning of the period	$	11,052	$	2,977