Revenue Recognition - Changes in contract assets (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2020	Mar. 31, 2019
Contract assets:
Unbilled receivables, Balance at Beginning of Period	$ 3,315	$ 3,279
Unbilled receivables, Revenue Recognized In Advance of Billings	183	1,059
Unbilled receivables, Billings	(273)	(420)
Unbilled receivables, Balance at End of Period	$ 3,225	$ 3,918