SUPPLEMENTAL BALANCE SHEET AND CASH FLOW INFORMATION (goodwill) (Details) - USD ($) $ in Thousands		3 Months Ended	12 Months Ended
		Sep. 30, 2019	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Changes in goodwill
Goodwill, gross, beginning of year			$ 1,287,193	$ 1,179,313
Accumulated impairment charges, beginning of year			(126,567)	(48,379)
Goodwill, net of accumulated impairment charges, beginning of year			1,160,626	1,130,934
Impairment charge (Note 8)		$ (357,741)	(357,741)	(78,188)
Goodwill resulting from acquisitions (Note 6)			4,174	105,907
Adjustment of assets held for sale				635
Currency translation adjustment			(806)	(2,845)
Goodwill, gross, end of period			1,288,795	1,287,193	$ 1,179,313
Accumulated impairment charges, end of period			(484,308)	(126,567)	(48,379)
Goodwill, net of accumulated impairment charges, end of period			804,487	1,160,626	1,130,934
2017 acquisitions [Member]
Changes in goodwill
Goodwill resulting from acquisitions (Note 6)	[1]				63,941
Measurement-period adjustments for prior year acquisitions (Note 6)				4,183
2018 acquisitions [Member]
Changes in goodwill
Goodwill resulting from acquisitions (Note 6)	[2]			104,140
Measurement-period adjustments for prior year acquisitions (Note 6)			(1,766)
Reportable business segments [Member] | Small Business Services [Member]
Changes in goodwill
Goodwill, gross, beginning of year			765,266	706,568
Accumulated impairment charges, beginning of year			(126,567)	(48,379)
Goodwill, net of accumulated impairment charges, beginning of year			638,699	658,189
Impairment charge (Note 8)			(242,267)	(78,188)
Goodwill resulting from acquisitions (Note 6)				59,488
Adjustment of assets held for sale				635
Currency translation adjustment			(806)	(2,845)
Goodwill, gross, end of period			764,120	765,266	706,568
Accumulated impairment charges, end of period			(368,834)	(126,567)	(48,379)
Goodwill, net of accumulated impairment charges, end of period			395,286	638,699	658,189
Reportable business segments [Member] | Small Business Services [Member] | 2017 acquisitions [Member]
Changes in goodwill
Measurement-period adjustments for prior year acquisitions (Note 6)				1,420
Reportable business segments [Member] | Small Business Services [Member] | 2018 acquisitions [Member]
Changes in goodwill
Measurement-period adjustments for prior year acquisitions (Note 6)			(340)
Reportable business segments [Member] | Financial Services [Member]
Changes in goodwill
Goodwill, gross, beginning of year			373,421	324,239
Accumulated impairment charges, beginning of year			0	0
Goodwill, net of accumulated impairment charges, beginning of year			373,421	324,239
Impairment charge (Note 8)			(115,474)
Goodwill resulting from acquisitions (Note 6)			4,174	46,419
Goodwill, gross, end of period			376,169	373,421	324,239
Accumulated impairment charges, end of period			(115,474)	0	0
Goodwill, net of accumulated impairment charges, end of period			260,695	373,421	324,239
Reportable business segments [Member] | Financial Services [Member] | 2017 acquisitions [Member]
Changes in goodwill
Measurement-period adjustments for prior year acquisitions (Note 6)				2,763
Reportable business segments [Member] | Financial Services [Member] | 2018 acquisitions [Member]
Changes in goodwill
Measurement-period adjustments for prior year acquisitions (Note 6)			(1,426)
Reportable business segments [Member] | Direct Checks [Member]
Changes in goodwill
Goodwill, gross, beginning of year			148,506	148,506
Accumulated impairment charges, beginning of year			0	0
Goodwill, net of accumulated impairment charges, beginning of year			148,506	148,506
Goodwill, gross, end of period			148,506	148,506	148,506
Accumulated impairment charges, end of period			0	0	0
Goodwill, net of accumulated impairment charges, end of period			$ 148,506	$ 148,506	$ 148,506

[1] Net tangible assets acquired and liabilities assumed for 2017 consisted primarily of accounts receivable, marketable securities, inventory and accrued liabilities of RDM and Digital Pacific. Amounts include measurement-period adjustments recorded in 2018 for the finalization of purchase accounting for several of the 2017 acquisitions. These adjustments increased goodwill $4,183, with the offset to various assets and liabilities, including deferred revenue, deferred income taxes and other long-term liabilities, as well as a decrease of $1,654 in customer list intangibles and an increase in internal-use software of $1,000.

[2] Net tangible assets acquired and liabilities assumed for 2018 consisted primarily of REMITCO accounts receivable and Logomix deferred income tax liabilities. Amounts include measurement-period adjustments recorded in 2019 for the finalization of purchase accounting for certain of the 2018 acquisitions. These adjustments decreased goodwill $1,766, with the offset to various assets and liabilities, including a $1,000 increase in customer list intangible assets.