2. Revenue: Schedule of changes in the contract assets and the contract liabilities (Details) $ in Thousands	3 Months Ended
	Mar. 31, 2019 USD ($)
Contract revenue recognized
Increase (Decrease) in Contract with Customer, Liability	$ (3,265)
Increase (Decrease) in Contract with Customer, Asset	(1,343)
Contract receivables recorded
Increase (Decrease) in Contract with Customer, Asset	384
Contract amount billed
Increase (Decrease) in Contract with Customer, Liability	$ 1,720