Segment Information - Revenue by Segment (Details) - USD ($) $ in Thousands	3 Months Ended	9 Months Ended
Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020
Segment Reporting Information [Line Items]
Total revenues	$ 482,764	$ 382,116	$ 1,353,004	$ 1,160,879
Interest income	183	1,620	1,219	4,468
Fleet Solutions
Segment Reporting Information [Line Items]
Total revenues	286,361	228,704	804,586	682,931
Interest income	178	1,304	1,194	3,205
Travel and Corporate Solutions
Segment Reporting Information [Line Items]
Total revenues	91,002	64,296	243,406	203,150
Interest income	2	12	12	265
Health and Employee Benefit Solutions
Segment Reporting Information [Line Items]
Total revenues	105,401	89,116	305,012	274,798
Interest income	3	304	13	998
Payment processing revenue
Segment Reporting Information [Line Items]
Total revenues	226,126	171,077	627,941	522,575
Payment processing revenue \| Fleet Solutions
Segment Reporting Information [Line Items]
Total revenues	130,006	102,418	367,032	305,888
Payment processing revenue \| Travel and Corporate Solutions
Segment Reporting Information [Line Items]
Total revenues	79,815	53,239	205,345	166,768
Payment processing revenue \| Health and Employee Benefit Solutions
Segment Reporting Information [Line Items]
Total revenues	16,305	15,420	55,564	49,919
Account servicing revenue
Segment Reporting Information [Line Items]
Total revenues	137,724	112,417	389,344	335,736
Account servicing revenue \| Fleet Solutions
Segment Reporting Information [Line Items]
Total revenues	43,671	39,350	125,955	115,252
Account servicing revenue \| Travel and Corporate Solutions
Segment Reporting Information [Line Items]
Total revenues	10,908	9,964	32,817	31,210
Account servicing revenue \| Health and Employee Benefit Solutions
Segment Reporting Information [Line Items]
Total revenues	83,145	63,103	230,572	189,274
Finance fee revenue
Segment Reporting Information [Line Items]
Total revenues	67,769	46,307	179,421	144,945
Finance fee revenue \| Fleet Solutions
Segment Reporting Information [Line Items]
Total revenues	67,529	46,129	178,627	143,934
Finance fee revenue \| Travel and Corporate Solutions
Segment Reporting Information [Line Items]
Total revenues	200	145	693	900
Finance fee revenue \| Health and Employee Benefit Solutions
Segment Reporting Information [Line Items]
Total revenues	40	33	101	111
Other revenue
Segment Reporting Information [Line Items]
Total revenues	51,145	52,315	156,298	157,623
Other revenue \| Fleet Solutions
Segment Reporting Information [Line Items]
Total revenues	45,155	40,807	132,972	117,857
Other revenue \| Travel and Corporate Solutions
Segment Reporting Information [Line Items]
Total revenues	79	948	4,551	4,272
Other revenue \| Health and Employee Benefit Solutions
Segment Reporting Information [Line Items]
Total revenues	$ 5,911	$ 10,560	$ 18,775	$ 35,494