Segment Information - Summarized Financial Information Reportable Segments (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Segment Reporting Information [Line Items]
Total revenues	$ 3,051,398	$ 2,613,375	$ 2,392,171
Investment income	1,099	2,811	5,780
Amortization	119,593	108,523	105,298
Depreciation	33,309	26,276	23,417
Interest expense	64,981	58,973	63,660
Income before income taxes	762,823	624,099	525,929
Total assets	9,795,443	8,966,492	7,622,821
Capital expenditures	45,045	70,700	73,108
Operating Segments | Retail
Segment Reporting Information [Line Items]
Total revenues	1,767,938	1,472,766	1,367,261
Investment income	278	163	149
Amortization	77,810	67,315	63,146
Depreciation	11,194	9,071	7,390
Interest expense	91,425	85,968	87,295
Income before income taxes	334,377	262,245	222,875
Total assets	5,040,706	7,093,627	6,413,459
Capital expenditures	8,093	13,175	12,497
Operating Segments | National Programs
Segment Reporting Information [Line Items]
Total revenues	701,850	610,640	518,384
Investment income	550	756	1,397
Amortization	27,357	27,166	25,482
Depreciation	9,839	8,658	6,791
Interest expense	11,381	20,597	16,690
Income before income taxes	242,334	182,892	143,737
Total assets	2,943,006	3,510,983	3,110,368
Capital expenditures	13,467	7,208	10,365
Operating Segments | Wholesale Brokerage
Segment Reporting Information [Line Items]
Total revenues	403,417	352,797	310,087
Investment income	155	184	178
Amortization	9,150	8,481	11,191
Depreciation	2,646	1,948	1,674
Interest expense	15,990	10,281	4,756
Income before income taxes	94,845	93,593	82,739
Total assets	1,154,373	1,791,717	1,390,250
Capital expenditures	1,612	3,324	6,171
Operating Segments | Services
Segment Reporting Information [Line Items]
Total revenues	178,860	174,012	193,781
Investment income	3	0	139
Amortization	5,276	5,561	5,479
Depreciation	1,484	1,424	1,229
Interest expense	2,899	4,142	4,404
Income before income taxes	28,257	27,994	40,337
Total assets	299,185	480,440	481,336
Capital expenditures	1,609	1,424	804
Segment Reconciling Items
Segment Reporting Information [Line Items]
Total revenues	(667)	3,160	2,658
Investment income	113	1,708	3,917
Amortization	0
Depreciation	8,146	5,175	6,333
Interest expense	(56,714)	(62,015)	(49,485)
Income before income taxes	63,010	57,375	36,241
Total assets	358,173	(3,910,275)	(3,772,592)
Capital expenditures	$ 20,264	$ 45,569	$ 43,271