Income taxes - Schedule of Components of (Provision) Benefit for Income Taxes (Details) - USD ($) $ in Thousands	3 Months Ended		12 Months Ended
	Mar. 31, 2019	Mar. 31, 2018	Mar. 31, 2020	Dec. 31, 2018	Dec. 31, 2017
Current:
U.S. federal	$ (13)		$ (2,681)	$ (2,414)	$ (2,058)
State	(139)		(1,066)	(948)	(369)
Foreign	(22)		5	(8)	0
Total current	(174)		(3,742)	(3,370)	(2,427)
Deferred:
U.S. federal	3,096		(2,532)	1,005	13,246
State	368		99	101	(21)
Foreign	(31)		(10)	(167)	208
Total deferred	3,433		(2,443)	939	13,433
Total (provision) benefit for income taxes	$ 3,259	$ (433)	$ (6,185)	$ (2,431)	$ 11,006