BUSINESS ACQUISITION (Details)					3 Months Ended					6 Months Ended
	Jun. 11, 2018 USD ($) payment	Sep. 19, 2017 USD ($) payment	Jun. 14, 2017 USD ($) payment	Nov. 17, 2016 USD ($) payment	Sep. 30, 2018 USD ($)	Jun. 30, 2018 USD ($)	Mar. 31, 2018 USD ($)	Sep. 30, 2017 USD ($)	Jun. 30, 2017 USD ($)	Jun. 30, 2018 USD ($) segment	Jun. 30, 2017 USD ($) segment	Dec. 31, 2017 USD ($)	Nov. 16, 2016 USD ($)
Business Acquisition
Goodwill						$ 124,903,000				$ 124,903,000		$ 113,368,000
Number of Reportable Segments | segment										1	1
Revenue						184,101,000			$ 152,773,000	$ 365,136,000	$ 285,288,000
Payment for Contingent Consideration Liability, Financing Activities										25,600,000	0
Current contingent consideration						7,283,000				7,283,000		46,576,000
Non-current contingent consideration						7,958,000				7,958,000		$ 11,273,000
Change in fair value of contingent consideration						(167,000)			9,393,000	(908,000)	18,139,000
Pro forma revenue						185,820,000			158,737,000	369,201,000	296,935,000
Pro forma net income from continuing operations						45,188,000			7,758,000	80,956,000	14,966,000
After tax contingent consideration tax						100,000			$ 5,600,000	700,000	10,900,000
Ovation
Business Acquisition
Initial cash consideration to acquire business	$ 12,200,000
Number of payments | payment	2
Purchase price consideration on acquisition date	$ 17,987,000
Contingent consideration	5,800,000
Working Capital						305,000				305,000
Property, Plant, and Equipment						106,000				106,000
Finite-Lived Intangibles	$ 8,700,000					8,700,000				8,700,000
Goodwill						11,535,000				11,535,000
Deferred Tax Liabilities Noncurrent						(2,659,000)				(2,659,000)
Acquired Finite-lived Intangible Assets, Weighted Average Useful Life	5 years 6 months
Revenue						500,000
Business Combination, Acquisition Related Costs						300,000
CompareCards
Business Acquisition
Initial cash consideration to acquire business				$ 80,700,000
Number of payments | payment				2
Contingent consideration range, maximum													$ 45,000,000
Purchase price consideration on acquisition date				$ 103,800,000
Contingent consideration													23,100,000
Payment for Contingent Consideration Liability, Financing Activities						22,500,000	$ 22,500,000
Change in fair value of contingent consideration						200,000				700,000
CompareCards | Cash Flows from Financing Activities
Business Acquisition
Payment for Contingent Consideration Liability, Financing Activities						600,000
CompareCards | Cash Flows from Operating Activities
Business Acquisition
Payment for Contingent Consideration Liability, Financing Activities						21,900,000
DepositAccounts
Business Acquisition
Initial cash consideration to acquire business			$ 24,000,000							0	24,000,000
Number of payments | payment			7
Contingent consideration range, maximum			$ 9,000,000
Purchase price consideration on acquisition date			29,000,000
Contingent consideration			5,000,000			5,300,000				5,300,000
Payment for Contingent Consideration Liability, Financing Activities						1,000,000
Current contingent consideration						4,400,000				4,400,000
Non-current contingent consideration						900,000				900,000
Change in fair value of contingent consideration						400,000				1,300,000
Contingent consideration payment								$ 1,000,000
Value of potential contingent consideration payments based on specified increases in federal funds interest rates			1,000,000
One-time contingent consideration performance payment			2,000,000
SnapCap
Business Acquisition
Initial cash consideration to acquire business		$ 11,900,000								10,000	$ 0
Number of payments | payment		3
Purchase price consideration on acquisition date		$ 18,200,000
Contingent consideration		6,300,000				4,100,000				4,100,000
Current contingent consideration						2,900,000				2,900,000
Non-current contingent consideration						1,200,000				1,200,000
Change in fair value of contingent consideration						$ 800,000				$ 2,900,000
Technology | Ovation
Business Acquisition
Finite-lived Intangible Assets Acquired	$ 6,000,000
Acquired Finite-lived Intangible Assets, Weighted Average Useful Life	7 years
Customer lists | Ovation
Business Acquisition
Finite-lived Intangible Assets Acquired	$ 1,700,000
Acquired Finite-lived Intangible Assets, Weighted Average Useful Life	1 year
Trade name and trademarks | Ovation
Business Acquisition
Finite-lived Intangible Assets Acquired	$ 1,000,000
Acquired Finite-lived Intangible Assets, Weighted Average Useful Life	4 years
Contingent earnout | Ovation
Business Acquisition
Contingent consideration range, minimum	$ 0
Contingent consideration range, maximum	4,375,000
Contingent earnout | CompareCards
Business Acquisition
Contingent consideration range, maximum													$ 22,500,000
Contingent earnout | SnapCap
Business Acquisition
Contingent consideration range, minimum		0
Contingent consideration range, maximum		3,000,000
Minimum
Business Acquisition
Contingent consideration	0	0	1,000,000
Maximum
Business Acquisition
Contingent consideration	$ 8,750,000	$ 9,000,000	$ 6,000,000
Subsequent Event | DepositAccounts
Business Acquisition
Payment for Contingent Consideration Liability, Financing Activities					$ 1,000,000