Segment Information - Revenue by Segment (Details) - USD ($) $ in Thousands	3 Months Ended	9 Months Ended
Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Segment Reporting Information [Line Items]
Payment processing revenue	$ 244,872		$ 721,411
Account servicing revenue	78,748	$ 71,322	236,168	$ 198,538
Finance fee revenue	53,703	50,879	154,958	136,336
Other revenue	67,368	56,099	187,206	160,935
Total revenues	382,690	324,002	1,108,395	919,243
Interest income	1,807	12,051	15,540	26,586
Fleet Solutions
Segment Reporting Information [Line Items]
Payment processing revenue	134,664		395,954
Account servicing revenue	42,810	44,858	128,039	122,238
Finance fee revenue	51,644	40,773	140,436	113,754
Other revenue	39,135	36,177	117,076	103,003
Total revenues	249,612	212,078	721,447	603,205
Interest income	1,092	944	3,127	2,764
Travel and Corporate Solutions
Segment Reporting Information [Line Items]
Payment processing revenue	64,528		181,381
Account servicing revenue	9,120	206	27,584	528
Finance fee revenue	670	87	1,157	469
Other revenue	18,675	16,556	46,201	43,414
Total revenues	82,810	61,026	225,353	163,739
Interest income	172	208	715	569
Health and Employee Benefit Solutions
Segment Reporting Information [Line Items]
Payment processing revenue	45,680		144,076
Account servicing revenue	26,818	26,258	80,545	75,772
Finance fee revenue	1,389	10,019	13,365	22,113
Other revenue	9,558	3,366	23,929	14,518
Total revenues	50,268	50,898	161,595	152,299
Interest income	543	10,899	11,698	23,253
Payment processing revenue
Segment Reporting Information [Line Items]
Payment processing revenue	182,871	145,702	530,063	423,434
Payment processing revenue \| Fleet Solutions
Segment Reporting Information [Line Items]
Payment processing revenue	116,023	90,270	335,896	264,210
Payment processing revenue \| Travel and Corporate Solutions
Segment Reporting Information [Line Items]
Payment processing revenue	54,345	44,177	150,411	119,328
Payment processing revenue \| Health and Employee Benefit Solutions
Segment Reporting Information [Line Items]
Payment processing revenue	$ 12,503	$ 11,255	$ 43,756	$ 39,896

Amount of operating interest income, including, but not limited to, amortization and accretion of premiums and discounts on securities.

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