ACQUISITIONS - Schedule of Recognized Identified Assets Acquired and Liabilities Assumed (Details) - USD ($) $ in Thousands	Dec. 31, 2019	Dec. 31, 2018	Jul. 31, 2018	Jan. 31, 2018	Dec. 31, 2017
Business Acquisition [Line Items]
Goodwill	$ 68,697	$ 99,108			$ 67,301
Intangibles		40,323
Pay Systems
Business Acquisition [Line Items]
Cash & cash equivalents				$ 764
Accounts receivable				56
Fixed assets				121
Inventory				0
Other assets				100
Funds held for clients				10,976
Goodwill				9,606
Intangibles				7,240
Total assets acquired				28,863
Accounts payable				85
Deferred tax liability				1,364
Accrued other liabilities				946
Deferred revenue				0
Client fund obligations				11,962
Total liabilities assumed				14,357
Net assets acquired				$ 14,506
USA Payroll
Business Acquisition [Line Items]
Cash & cash equivalents			$ 470
Accounts receivable			104
Fixed assets			98
Inventory			0
Other assets			5
Funds held for clients			20,439
Goodwill			12,644
Intangibles			17,643
Total assets acquired			51,403
Accounts payable			39
Deferred tax liability			3,622
Accrued other liabilities			376
Deferred revenue			0
Client fund obligations			20,439
Total liabilities assumed			24,476
Net assets acquired			$ 26,927
Others
Business Acquisition [Line Items]
Cash & cash equivalents		643
Accounts receivable		2,395
Fixed assets		428
Inventory		121
Other assets		995
Funds held for clients		14,013
Goodwill		11,966
Intangibles		15,440
Total assets acquired		46,001
Accounts payable		880
Deferred tax liability		2,036
Accrued other liabilities		2,335
Deferred revenue		1,289
Client fund obligations		14,000
Total liabilities assumed		20,540
Net assets acquired		25,461
2018 Acquisitions
Business Acquisition [Line Items]
Cash & cash equivalents		1,877
Accounts receivable		2,555
Fixed assets		647
Inventory		121
Other assets		1,100
Funds held for clients		45,428
Goodwill		34,216
Intangibles		40,323
Total assets acquired		126,267
Accounts payable		1,004
Deferred tax liability		7,022
Accrued other liabilities		3,657
Deferred revenue		1,289
Client fund obligations		46,401
Total liabilities assumed		59,373
Net assets acquired		$ 66,894