ACQUISITIONS - Resource Water Acquisition - Purchase price allocation (Details) - USD ($) $ in Thousands	Sep. 15, 2017	Mar. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Less: identified assets acquired and liabilities assumed
Goodwill		$ 275,795	$ 273,421	$ 12,242
Resource Water Acquisition
Consideration transferred
Cash paid	$ 6,586
Total consideration transferred	8,966
Less: identified assets acquired and liabilities assumed
Working capital	1,189
Fixed assets	3,485
Total identifiable net assets acquired	7,072
Goodwill	1,894
Fair value allocated to net assets acquired	8,966
Resource Water Acquisition | Class A Common Stock
Consideration transferred
Common stock issued	$ 2,380
Less: identified assets acquired and liabilities assumed
Shares issued in Merger Agreement	156,909
Resource Water Acquisition | Customer relationships
Less: identified assets acquired and liabilities assumed
Intangible assets	$ 1,933
Resource Water Acquisition | Other
Less: identified assets acquired and liabilities assumed
Intangible assets	$ 465