INCOME TAX - Change in Valuation Allowance (Details) - USD ($) $ in Thousands	7 Months Ended	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2017	May 31, 2016	May 31, 2015
Movement in Deferred Tax Valuation Allowance [Roll Forward]
Valuation allowance, beginning of period	$ (15,119)	$ (16,611)	$ (3,823)	$ (7,199)
Valuation allowance, end of period	(16,611)	(16,550)	(15,119)	(3,823)
Net operating loss carryforwards
Movement in Deferred Tax Valuation Allowance [Roll Forward]
Valuation allowance, change	(1,504)	(3,793)	(4,500)
Net operating loss carryforwards \| Heartland Payment Systems, Inc
Movement in Deferred Tax Valuation Allowance [Roll Forward]
Valuation allowance, change			(4,474)
Net operating loss carryforwards \| Foreign Tax Authority
Movement in Deferred Tax Valuation Allowance [Roll Forward]
Valuation allowance, change		(6,469)		3,387
Other
Movement in Deferred Tax Valuation Allowance [Roll Forward]
Valuation allowance, change		7,140	98	$ (11)
Income tax credit carryforward
Movement in Deferred Tax Valuation Allowance [Roll Forward]
Valuation allowance, change		(685)
Income tax credit carryforward \| Foreign Tax Authority
Movement in Deferred Tax Valuation Allowance [Roll Forward]
Valuation allowance, change			(7,140)
Capital loss
Movement in Deferred Tax Valuation Allowance [Roll Forward]
Valuation allowance, change	$ 12		(1,526)
Net unrealized capital loss
Movement in Deferred Tax Valuation Allowance [Roll Forward]
Valuation allowance, change			$ 1,746
Rate change on domestic net operating loss and capital loss carryforwards
Movement in Deferred Tax Valuation Allowance [Roll Forward]
Valuation allowance, change		$ 3,868