ACQUISITIONS - GRR Acquisition - Purchase price allocation (Details) - USD ($) $ in Thousands	Mar. 10, 2017	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Less: identified assets acquired and liabilities assumed
Goodwill		$ 266,934	$ 273,801	$ 273,421
GRR Acquisition
Consideration transferred
Cash paid	$ 53,032
Class A Common Stock (274,998 shares)	5,500
Assumed liabilities	1,106
Total consideration transferred	59,638
Less: identified assets acquired and liabilities assumed
Working capital	7,728
Fixed assets	13,225
Total identifiable net assets acquired	47,589
Goodwill	12,049
Fair value allocated to net assets acquired	$ 59,638
Shares issued in Merger Agreement	274,998
GRR Acquisition | Customer relationships
Less: identified assets acquired and liabilities assumed
Intangible assets	$ 21,484
GRR Acquisition | Other intangibles
Less: identified assets acquired and liabilities assumed
Intangible assets	$ 5,152