Business Combinations - Purchase Price Allocation for Current Year Acquisitions and Adjustments Made for Prior Year Acquisitions (Details) - USD ($) $ in Thousands																									12 Months Ended
	Dec. 31, 2021	Dec. 01, 2021	Oct. 01, 2021	Sep. 01, 2021	May 01, 2021	Jan. 01, 2021	Dec. 31, 2020	Dec. 01, 2020	Nov. 01, 2020	Oct. 01, 2020	Sep. 01, 2020	Aug. 01, 2020	Jul. 01, 2020	May 01, 2020	Apr. 01, 2020	Mar. 01, 2020	Jan. 01, 2020	Oct. 01, 2019	Aug. 01, 2019	Jul. 01, 2019	Jun. 01, 2019	May 01, 2019	Mar. 01, 2019	Feb. 01, 2019	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Business Combination Separately Recognized Transactions [Line Items]
Cash paid																									$ 424,600	$ 722,500
Common Stock Issued																									9,892	30,120	$ 20,000
Net assets acquired	$ 549,452						$ 893,162																		549,452	893,162	471,267
O'Leary Insurances (O'Leary)
Business Combination Separately Recognized Transactions [Line Items]
Net assets acquired						$ 137,648
O'Leary Insurances (O'Leary) | Retail
Business Combination Separately Recognized Transactions [Line Items]
Effective date of acquisition						Jan. 01, 2021
Cash paid						$ 117,408
Common Stock Issued						4,892
Other payable						0
Recorded earn-out payable						15,348
Net assets acquired						137,648
Maximum potential earn- out payable						$ 30,575
Piper Jordan LLC (Piper)
Business Combination Separately Recognized Transactions [Line Items]
Net assets acquired					$ 54,679
Piper Jordan LLC (Piper) | Retail
Business Combination Separately Recognized Transactions [Line Items]
Effective date of acquisition					May 01, 2021
Cash paid					$ 43,428
Common Stock Issued					0
Other payable					1,397
Recorded earn-out payable					9,854
Net assets acquired					$ 54,679
Maximum potential earn- out payable	15,000																								15,000
Berkshire Insurance Group, Inc. (Berkshire)
Business Combination Separately Recognized Transactions [Line Items]
Net assets acquired				$ 41,500
Berkshire Insurance Group, Inc. (Berkshire) | Retail
Business Combination Separately Recognized Transactions [Line Items]
Effective date of acquisition				Sep. 01, 2021
Cash paid				$ 41,500
Common Stock Issued				0
Other payable				0
Recorded earn-out payable				0
Net assets acquired				41,500
Maximum potential earn- out payable				0
AGIS Network, Inc. (AGIS)
Business Combination Separately Recognized Transactions [Line Items]
Net assets acquired				$ 36,056
AGIS Network, Inc. (AGIS) | Retail
Business Combination Separately Recognized Transactions [Line Items]
Effective date of acquisition				Sep. 01, 2021
Cash paid				$ 11,203
Common Stock Issued				0
Other payable				24,114
Recorded earn-out payable				739
Net assets acquired				36,056
Maximum potential earn- out payable				$ 12,289
Winston Financial Services, Inc. (Winston)
Business Combination Separately Recognized Transactions [Line Items]
Net assets acquired			$ 108,612
Winston Financial Services, Inc. (Winston) | Retail
Business Combination Separately Recognized Transactions [Line Items]
Effective date of acquisition			Oct. 01, 2021
Cash paid			$ 79,461
Common Stock Issued			5,000
Other payable			7,724
Recorded earn-out payable			16,427
Net assets acquired			108,612
Maximum potential earn- out payable			29,000
Remedy Analytics, Inc. (Remedy)
Business Combination Separately Recognized Transactions [Line Items]
Net assets acquired			$ 48,599
Remedy Analytics, Inc. (Remedy) | Retail
Business Combination Separately Recognized Transactions [Line Items]
Effective date of acquisition			Oct. 01, 2021
Cash paid			$ 40,762
Common Stock Issued			0
Other payable			473
Recorded earn-out payable			7,364
Net assets acquired			48,599
Maximum potential earn- out payable			25,000
Heacock Insurance Group, LLC (Heacock)
Business Combination Separately Recognized Transactions [Line Items]
Net assets acquired			$ 20,603
Heacock Insurance Group, LLC (Heacock) | Retail
Business Combination Separately Recognized Transactions [Line Items]
Effective date of acquisition			Oct. 01, 2021
Cash paid			$ 18,248
Common Stock Issued			0
Other payable			455
Recorded earn-out payable			1,900
Net assets acquired			20,603
Maximum potential earn- out payable			$ 6,000
Corporate Insurance Advisors, L.L.C. (CIA)
Business Combination Separately Recognized Transactions [Line Items]
Net assets acquired		$ 22,037
Corporate Insurance Advisors, L.L.C. (CIA) | Retail
Business Combination Separately Recognized Transactions [Line Items]
Effective date of acquisition		Dec. 01, 2021
Cash paid		$ 15,314
Common Stock Issued		0
Other payable		181
Recorded earn-out payable		6,542
Net assets acquired		22,037
Maximum potential earn- out payable		14,000
Rainmaker Advisory, LLC (Rainmaker)
Business Combination Separately Recognized Transactions [Line Items]
Net assets acquired		$ 20,887
Rainmaker Advisory, LLC (Rainmaker) | Retail
Business Combination Separately Recognized Transactions [Line Items]
Effective date of acquisition		Dec. 01, 2021
Cash paid		$ 14,174
Common Stock Issued		0
Other payable		776
Recorded earn-out payable		5,937
Net assets acquired		20,887
Maximum potential earn- out payable		$ 10,000
HARCO Insurance Services, Inc. (HARCO)
Business Combination Separately Recognized Transactions [Line Items]
Net assets acquired	$ 29,689																								29,689
HARCO Insurance Services, Inc. (HARCO) | Retail
Business Combination Separately Recognized Transactions [Line Items]
Effective date of acquisition	Dec. 31, 2021
Cash paid	$ 24,266
Common Stock Issued	0
Other payable	1,000
Recorded earn-out payable	4,423
Net assets acquired	29,689																								29,689
Maximum potential earn- out payable	7,350																								7,350
Special Risk Insurance Managers Ltd. (Special Risk) | National Programs
Business Combination Separately Recognized Transactions [Line Items]
Effective date of acquisition																	Jan. 01, 2020
Cash paid																	$ 70,156
Common Stock Issued																	0
Other payable																	0
Recorded earn-out payable																	9,859
Net assets acquired																	80,015
Maximum potential earn- out payable																	14,650
Texas All Risk General Agency, Inc. et al (Texas Risk)
Business Combination Separately Recognized Transactions [Line Items]
Net assets acquired																	$ 10,980
Texas All Risk General Agency, Inc. et al (Texas Risk) | Wholesale Brokerage
Business Combination Separately Recognized Transactions [Line Items]
Effective date of acquisition																	Jan. 01, 2020
Cash paid																	$ 10,511
Common Stock Issued																	0
Other payable																	159
Recorded earn-out payable																	310
Net assets acquired																	10,980
Maximum potential earn- out payable																	$ 1,150
The Colonial Group, Inc. et al (Colonial)
Business Combination Separately Recognized Transactions [Line Items]
Net assets acquired																$ 37,141
The Colonial Group, Inc. et al (Colonial) | Wholesale Brokerage
Business Combination Separately Recognized Transactions [Line Items]
Effective date of acquisition																Mar. 01, 2020
Cash paid																$ 29,037
Common Stock Issued																0
Other payable																527
Recorded earn-out payable																7,577
Net assets acquired																37,141
Maximum potential earn- out payable																10,150
RLA Insurance Intermediaries, LLC (RLA)
Business Combination Separately Recognized Transactions [Line Items]
Net assets acquired																$ 54,969
RLA Insurance Intermediaries, LLC (RLA) | Wholesale Brokerage
Business Combination Separately Recognized Transactions [Line Items]
Effective date of acquisition																Mar. 01, 2020
Cash paid																$ 42,496
Common Stock Issued																0
Other payable																786
Recorded earn-out payable																11,687
Net assets acquired																54,969
Maximum potential earn- out payable																$ 22,500
Dealer Financial Services of N.C., LLC d/b/a The Sterling Group (Sterling)
Business Combination Separately Recognized Transactions [Line Items]
Net assets acquired															$ 23,770
Dealer Financial Services of N.C., LLC d/b/a The Sterling Group (Sterling) | Retail
Business Combination Separately Recognized Transactions [Line Items]
Effective date of acquisition															Apr. 01, 2020
Cash paid															$ 19,341
Common Stock Issued															0
Other payable															300
Recorded earn-out payable															4,129
Net assets acquired															23,770
Maximum potential earn- out payable															$ 5,400
LP Insurance Services, LLC (LP)
Business Combination Separately Recognized Transactions [Line Items]
Net assets acquired														$ 149,660
LP Insurance Services, LLC (LP) | National Programs
Business Combination Separately Recognized Transactions [Line Items]
Effective date of acquisition														May 01, 2020
Cash paid														$ 115,948
Common Stock Issued														10,000
Other payable														318
Recorded earn-out payable														23,394
Net assets acquired														149,660
Maximum potential earn- out payable														$ 75,850
First Resource, Inc. (First)
Business Combination Separately Recognized Transactions [Line Items]
Net assets acquired													$ 14,926
First Resource, Inc. (First) | Retail
Business Combination Separately Recognized Transactions [Line Items]
Effective date of acquisition													Jul. 01, 2020
Cash paid													$ 10,700
Common Stock Issued													0
Other payable													450
Recorded earn-out payable													3,776
Net assets acquired													14,926
Maximum potential earn- out payable													$ 5,800
Buiten & Associates, LLC (Buiten)
Business Combination Separately Recognized Transactions [Line Items]
Net assets acquired												$ 46,848
Buiten & Associates, LLC (Buiten) | Retail
Business Combination Separately Recognized Transactions [Line Items]
Effective date of acquisition												Aug. 01, 2020
Cash paid												$ 38,225
Common Stock Issued												0
Other payable												1,175
Recorded earn-out payable												7,448
Net assets acquired												46,848
Maximum potential earn- out payable												14,175
Amity Insurance, Inc. (Amity)
Business Combination Separately Recognized Transactions [Line Items]
Net assets acquired												$ 18,880
Amity Insurance, Inc. (Amity) | Retail
Business Combination Separately Recognized Transactions [Line Items]
Effective date of acquisition												Aug. 01, 2020
Cash paid												$ 14,820
Common Stock Issued												2,000
Other payable												200
Recorded earn-out payable												1,860
Net assets acquired												18,880
Maximum potential earn- out payable												$ 4,060
Frank E. Neal & Co., Inc. (Neal)
Business Combination Separately Recognized Transactions [Line Items]
Net assets acquired											$ 41,786
Frank E. Neal & Co., Inc. (Neal) | Retail
Business Combination Separately Recognized Transactions [Line Items]
Effective date of acquisition											Sep. 01, 2020
Cash paid											$ 32,589
Common Stock Issued											3,120
Other payable											345
Recorded earn-out payable											5,732
Net assets acquired											41,786
Maximum potential earn- out payable											10,325
BrookStone Insurance Group, LLC (BrookStone)
Business Combination Separately Recognized Transactions [Line Items]
Net assets acquired											$ 13,088
BrookStone Insurance Group, LLC (BrookStone) | Retail
Business Combination Separately Recognized Transactions [Line Items]
Effective date of acquisition											Sep. 01, 2020
Cash paid											$ 12,030
Common Stock Issued											0
Other payable											0
Recorded earn-out payable											1,058
Net assets acquired											13,088
Maximum potential earn- out payable											$ 1,878
VAS GenPar, LLC (VAS)
Business Combination Separately Recognized Transactions [Line Items]
Net assets acquired										$ 152,523
VAS GenPar, LLC (VAS) | Retail
Business Combination Separately Recognized Transactions [Line Items]
Effective date of acquisition										Oct. 01, 2020
Cash paid										$ 114,249
Common Stock Issued										15,000
Other payable										0
Recorded earn-out payable										23,274
Net assets acquired										152,523
Maximum potential earn- out payable										48,000
Bright & Associates, Inc. (Bright)
Business Combination Separately Recognized Transactions [Line Items]
Net assets acquired										$ 17,639
Bright & Associates, Inc. (Bright) | Retail
Business Combination Separately Recognized Transactions [Line Items]
Effective date of acquisition										Oct. 01, 2020
Cash paid										$ 12,528
Common Stock Issued										0
Other payable										1,257
Recorded earn-out payable										3,854
Net assets acquired										17,639
Maximum potential earn- out payable										5,775
J.E. Brown & Associates Insurance Services, Inc. (J.E. Brown)
Business Combination Separately Recognized Transactions [Line Items]
Net assets acquired										$ 40,308
J.E. Brown & Associates Insurance Services, Inc. (J.E. Brown) | Wholesale Brokerage
Business Combination Separately Recognized Transactions [Line Items]
Effective date of acquisition										Oct. 01, 2020
Cash paid										$ 33,331
Common Stock Issued										0
Other payable										1,030
Recorded earn-out payable										5,947
Net assets acquired										40,308
Maximum potential earn- out payable										$ 10,425
CoverHound, Inc. and CyberPolicy, Inc. (CoverHound)
Business Combination Separately Recognized Transactions [Line Items]
Net assets acquired									$ 28,195
CoverHound, Inc. and CyberPolicy, Inc. (CoverHound) | Retail
Business Combination Separately Recognized Transactions [Line Items]
Effective date of acquisition									Nov. 01, 2020
Cash paid									$ 27,595
Common Stock Issued									0
Other payable									600
Recorded earn-out payable									0
Net assets acquired									28,195
Maximum potential earn- out payable									$ 0
MAJ Companies, Ltd. (MAJ)
Business Combination Separately Recognized Transactions [Line Items]
Net assets acquired								$ 21,378
MAJ Companies, Ltd. (MAJ) | Retail
Business Combination Separately Recognized Transactions [Line Items]
Effective date of acquisition								Dec. 01, 2020
Cash paid								$ 19,072
Common Stock Issued								0
Other payable								300
Recorded earn-out payable								2,006
Net assets acquired								21,378
Maximum potential earn- out payable								6,475
South & Western General Agency, Inc. (South & Western)
Business Combination Separately Recognized Transactions [Line Items]
Net assets acquired								$ 78,160
South & Western General Agency, Inc. (South & Western) | Wholesale Brokerage
Business Combination Separately Recognized Transactions [Line Items]
Effective date of acquisition								Dec. 01, 2020
Cash paid								$ 69,673
Common Stock Issued								0
Other payable								1,193
Recorded earn-out payable								7,294
Net assets acquired								78,160
Maximum potential earn- out payable								$ 18,000
Berry Insurance Group, Inc. (Berry)
Business Combination Separately Recognized Transactions [Line Items]
Net assets acquired							$ 39,020																			39,020
Berry Insurance Group, Inc. (Berry) | Retail
Business Combination Separately Recognized Transactions [Line Items]
Effective date of acquisition							Dec. 31, 2020
Cash paid							$ 35,326
Common Stock Issued							0
Other payable							0
Recorded earn-out payable							3,694
Net assets acquired							39,020																			39,020
Maximum potential earn- out payable							6,500																			6,500
Smith Insurance Associates, Inc. (Smith)
Business Combination Separately Recognized Transactions [Line Items]
Net assets acquired																								$ 22,833
Smith Insurance Associates, Inc. (Smith) | Retail
Business Combination Separately Recognized Transactions [Line Items]
Effective date of acquisition																								Feb. 01, 2019
Cash paid																								$ 20,129
Common Stock Issued																								0
Other payable																								0
Recorded earn-out payable																								2,704
Net assets acquired																								22,833
Maximum potential earn- out payable																								4,550
Donald P. Pipino Company, LTD (Pipino)
Business Combination Separately Recognized Transactions [Line Items]
Net assets acquired																								$ 26,376
Donald P. Pipino Company, LTD (Pipino) | Retail
Business Combination Separately Recognized Transactions [Line Items]
Effective date of acquisition																								Feb. 01, 2019
Cash paid																								$ 16,420
Common Stock Issued																								0
Other payable																								135
Recorded earn-out payable																								9,821
Net assets acquired																								26,376
Maximum potential earn- out payable																								$ 12,996
AGA Enterprises, LLC d/b/a Cossio Insurance Agency (Cossio)
Business Combination Separately Recognized Transactions [Line Items]
Net assets acquired																							$ 14,696
AGA Enterprises, LLC d/b/a Cossio Insurance Agency (Cossio) | Retail
Business Combination Separately Recognized Transactions [Line Items]
Effective date of acquisition																							Mar. 01, 2019
Cash paid																							$ 13,990
Common Stock Issued																							0
Other payable																							10
Recorded earn-out payable																							696
Net assets acquired																							14,696
Maximum potential earn- out payable																							2,000
Medval, LLC (Medval)
Business Combination Separately Recognized Transactions [Line Items]
Net assets acquired																							$ 30,890
Medval, LLC (Medval) | Services
Business Combination Separately Recognized Transactions [Line Items]
Effective date of acquisition																							Mar. 01, 2019
Cash paid																							$ 29,106
Common Stock Issued																							0
Other payable																							100
Recorded earn-out payable																							1,684
Net assets acquired																							30,890
Maximum potential earn- out payable																							$ 2,500
United Development Systems, Inc. (United)
Business Combination Separately Recognized Transactions [Line Items]
Net assets acquired																						$ 22,643
United Development Systems, Inc. (United) | Retail
Business Combination Separately Recognized Transactions [Line Items]
Effective date of acquisition																						May 01, 2019
Cash paid																						$ 18,987
Common Stock Issued																						0
Other payable																						388
Recorded earn-out payable																						3,268
Net assets acquired																						22,643
Maximum potential earn- out payable																						$ 8,625
Twinbrook Insurance Brokerage, Inc. (Twinbrook)
Business Combination Separately Recognized Transactions [Line Items]
Net assets acquired																					$ 28,216
Twinbrook Insurance Brokerage, Inc. (Twinbrook) | Retail
Business Combination Separately Recognized Transactions [Line Items]
Effective date of acquisition																					Jun. 01, 2019
Cash paid																					$ 26,251
Common Stock Issued																					0
Other payable																					400
Recorded earn-out payable																					1,565
Net assets acquired																					28,216
Maximum potential earn- out payable																					$ 5,073
Innovative Risk Solutions, Inc. (IRS)
Business Combination Separately Recognized Transactions [Line Items]
Net assets acquired																				$ 35,009
Innovative Risk Solutions, Inc. (IRS) | Retail
Business Combination Separately Recognized Transactions [Line Items]
Effective date of acquisition																				Jul. 01, 2019
Cash paid																				$ 26,435
Common Stock Issued																				0
Other payable																				2,465
Recorded earn-out payable																				6,109
Net assets acquired																				35,009
Maximum potential earn- out payable																				$ 9,000
WBR Insurance Agency, LLC et al (WBR)
Business Combination Separately Recognized Transactions [Line Items]
Net assets acquired																			$ 13,067
WBR Insurance Agency, LLC et al (WBR) | Retail
Business Combination Separately Recognized Transactions [Line Items]
Effective date of acquisition																			Aug. 01, 2019
Cash paid																			$ 10,667
Common Stock Issued																			0
Other payable																			203
Recorded earn-out payable																			2,197
Net assets acquired																			13,067
Maximum potential earn- out payable																			4,575
West Ridge Insurance Agency, Inc. d/b/a Yozell Associates (Yozell)
Business Combination Separately Recognized Transactions [Line Items]
Net assets acquired																			$ 14,268
West Ridge Insurance Agency, Inc. d/b/a Yozell Associates (Yozell) | Retail
Business Combination Separately Recognized Transactions [Line Items]
Effective date of acquisition																			Aug. 01, 2019
Cash paid																			$ 13,030
Common Stock Issued																			0
Other payable																			470
Recorded earn-out payable																			768
Net assets acquired																			14,268
Maximum potential earn- out payable																			6,730
CKP Insurance, LLC (CKP)
Business Combination Separately Recognized Transactions [Line Items]
Net assets acquired																			$ 151,283
CKP Insurance, LLC (CKP) | Retail
Business Combination Separately Recognized Transactions [Line Items]
Effective date of acquisition																			Aug. 01, 2019
Cash paid																			$ 89,190
Common Stock Issued																			20,000
Other payable																			4,000
Recorded earn-out payable																			38,093
Net assets acquired																			151,283
Maximum potential earn- out payable																			$ 76,500
Poole Professional Ltd. Insurance Agents and Brokers et al (Poole)
Business Combination Separately Recognized Transactions [Line Items]
Net assets acquired																		$ 36,989
Poole Professional Ltd. Insurance Agents and Brokers et al (Poole) | Retail
Business Combination Separately Recognized Transactions [Line Items]
Effective date of acquisition																		Oct. 01, 2019
Cash paid																		$ 32,358
Common Stock Issued																		0
Other payable																		75
Recorded earn-out payable																		4,556
Net assets acquired																		36,989
Maximum potential earn- out payable																		6,850
VerHagen Glendenning & Walker LLP (VGW)
Business Combination Separately Recognized Transactions [Line Items]
Net assets acquired																		$ 26,915
VerHagen Glendenning & Walker LLP (VGW) | Retail
Business Combination Separately Recognized Transactions [Line Items]
Effective date of acquisition																		Oct. 01, 2019
Cash paid																		$ 23,032
Common Stock Issued																		0
Other payable																		1,498
Recorded earn-out payable																		2,385
Net assets acquired																		26,915
Maximum potential earn- out payable																		$ 8,170
Other Acquisitions
Business Combination Separately Recognized Transactions [Line Items]
Net assets acquired	29,142						23,876																		29,142	23,876	48,082
Other Acquisitions | Various
Business Combination Separately Recognized Transactions [Line Items]
Cash paid							14,888																		18,849		36,665
Common Stock Issued							0																		0		0
Other payable							490																		3,066		2,391
Recorded earn-out payable							8,498																		7,227		9,026
Net assets acquired	29,142						23,876																		29,142	23,876	48,082
Maximum potential earn- out payable	13,118						12,337																		13,118	12,337	14,454
2021 Acquisition
Business Combination Separately Recognized Transactions [Line Items]
Cash paid																									424,613
Common Stock Issued																									9,892
Other payable																									39,186
Recorded earn-out payable																									75,761
Net assets acquired	549,452																								549,452
Maximum potential earn- out payable	$ 162,332																								$ 162,332
2020 Acquisition
Business Combination Separately Recognized Transactions [Line Items]
Cash paid																										722,515
Common Stock Issued																										30,120
Other payable																										9,130
Recorded earn-out payable																										131,397
Net assets acquired							893,162																			893,162
Maximum potential earn- out payable							$ 273,450																			$ 273,450
2019 Acquisition
Business Combination Separately Recognized Transactions [Line Items]
Cash paid																											356,260
Common Stock Issued																											20,000
Other payable																											12,135
Recorded earn-out payable																											82,872
Net assets acquired																											471,267
Maximum potential earn- out payable																											$ 162,023