CONSOLIDATED STATEMENTS OF CASH FLOWS - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Cash flows from operating activities:
Net income	$ 587,104	$ 480,483	$ 398,514
Adjustments to reconcile net income to net cash provided by operating activities:
Amortization	119,593	108,523	105,298
Depreciation	33,309	26,276	23,417
Non-cash stock-based compensation	61,018	59,749	46,994
Change in estimated acquisition earn-out payables	40,445	(4,458)	(1,366)
Deferred income taxes	33,616	15,943	12,383
Amortization of debt discount and disposal of deferred financing costs	2,839	2,319	2,054
Accretion of discounts and premiums, investments	171	48	(5)
(Gain)/loss on sales of investments, fixed assets and customer accounts	(7,096)	(831)	(9,550)
Payments on acquisition earn-outs in excess of original estimated payables	(21,060)	(4,532)	(351)
Effect of changes in foreign exchange rate changes	494
Changes in operating assets and liabilities, net of effect from acquisitions and divestitures:
Premiums, commissions and fees receivable (increase) decrease	(72,843)	(135,367)	(86,778)
Reinsurance recoverables (increase) decrease	(19,637)	15,036	6,891
Prepaid reinsurance premiums (increase) decrease	(14,607)	(11,594)	(28,101)
Other assets (increase) decrease	(53,746)	(42,731)	(46,520)
Premiums payable to insurance companies (increase) decrease	127,991	158,775	148,658
Premium deposits and credits due customers increase (decrease)	19,581	(12,886)	7,820
Losses and loss adjustment reserve increase (decrease)	19,637	(15,036)	(6,707)
Unearned premiums increase (decrease)	14,607	11,594	28,101
Accounts payable increase (decrease)	51,404	107,754	17,800
Accrued expenses and other liabilities increase (decrease)	66,782	34,716	43,330
Other liabilities increase (decrease)	(47,133)	(72,134)	16,298
Net cash provided by operating activities	942,469	721,647	678,180
Cash flows from investing activities:
Additions to fixed assets	(45,045)	(70,700)	(73,108)
Payments for businesses acquired, net of cash acquired	(366,780)	(694,842)	(353,043)
Proceeds from sales of fixed assets and customer accounts	16,735	9,615	21,592
Purchases of investments	(12,375)	(14,168)	(17,520)
Proceeds from sales of investments	10,785	11,025	8,494
Net cash used in investing activities	(396,680)	(759,070)	(413,585)
Cash flows from financing activities:
Payments on acquisition earn-outs	(62,521)	(24,977)	(9,566)
Proceeds from long-term debt		700,000	350,000
Payments on long-term debt	(73,125)	(55,000)	(50,000)
Deferred debt issuance costs	(2,683)	(6,756)	(3,701)
Borrowings on revolving credit facilities		250,000	100,000
Payments on revolving credit facilities		(350,000)	(350,000)
Issuances of common stock for employee stock benefit plans	34,026	30,104	24,999
Repurchase of stock benefit plan shares for employees to fund tax withholdings	(49,783)	(41,321)	(10,933)
Purchase of treasury stock	(82,564)	(55,095)	(58,671)
Settlement of accelerated share repurchase program			20,000
Cash dividends paid	(107,229)	(100,592)	(91,344)
Net cash (used in) provided by financing activities	(343,879)	346,363	(79,216)
Effect of foreign exchange rate cash changes	(3,569)
Net increase (decrease) in cash and cash equivalents inclusive of restricted cash	198,341	308,940	185,379
Cash and cash equivalents inclusive of restricted cash at beginning of period	1,271,915	962,975	777,596
Cash and cash equivalents inclusive of restricted cash at end of period	$ 1,470,256	$ 1,271,915	$ 962,975