CONSOLIDATED STATEMENTS OF CASH FLOWS - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Cash flows from operating activities:
Net income	$ 480,483	$ 398,514	$ 344,255
Adjustments to reconcile net income to net cash provided by operating activities:
Amortization	108,523	105,298	86,544
Depreciation	26,276	23,417	22,834
Non-cash stock-based compensation	59,749	46,994	33,519
Change in estimated acquisition earn-out payables	(4,458)	(1,366)	2,969
Deferred income taxes	15,943	12,383	15,008
Amortization of debt discount and disposal of deferred financing costs	2,319	2,054	1,627
Accretion of discounts and premiums, investments	48	(5)	(10)
(Gain)/loss on sales of investments, fixed assets and customer accounts	(831)	(9,550)	(1,934)
Payments on acquisition earn-outs in excess of original estimated payables	(4,532)	(351)	(12,538)
Changes in operating assets and liabilities, net of effect from acquisitions and divestitures:
Premiums, commissions and fees receivable (increase) decrease	(135,367)	(86,778)	(93,630)
Reinsurance recoverables (increase) decrease	15,036	6,891	412,424
Prepaid reinsurance premiums (increase) decrease	(11,594)	(28,101)	(16,903)
Other assets (increase) decrease	(42,731)	(46,520)	(22,440)
Premiums payable to insurance companies (increase) decrease	158,775	148,658	141,169
Premium deposits and credits due customers increase (decrease)	(12,886)	7,820	13,792
Losses and loss adjustment reserve increase (decrease)	(15,036)	(6,707)	(411,509)
Unearned premiums increase (decrease)	11,594	28,101	16,903
Accounts payable increase (decrease)	107,754	17,800	21,880
Accrued expenses and other liabilities increase (decrease)	34,716	43,330	22,801
Other liabilities increase (decrease)	(72,134)	16,298	(9,232)
Net cash provided by operating activities	721,647	678,180	567,529
Cash flows from investing activities:
Additions to fixed assets	(70,700)	(73,108)	(41,520)
Payments for businesses acquired, net of cash acquired	(694,842)	(353,043)	(923,874)
Proceeds from sales of fixed assets and customer accounts	9,615	21,592	4,984
Purchases of investments	(14,168)	(17,520)	(9,284)
Proceeds from sales of investments	11,025	8,494	17,923
Net cash used in investing activities	(759,070)	(413,585)	(951,771)
Cash flows from financing activities:
Payments on acquisition earn-outs	(24,977)	(9,566)	(14,059)
Proceeds from long-term debt	700,000	350,000	300,000
Payments on long-term debt	(55,000)	(50,000)	(120,000)
Deferred debt issuance costs	(6,756)	(3,701)	(778)
Borrowings on revolving credit facilities	250,000	100,000	600,000
Payments on revolving credit facilities	(350,000)	(350,000)	(250,000)
Issuances of common stock for employee stock benefit plans	30,104	24,999	19,432
Repurchase of stock benefit plan shares for employees to fund tax withholdings	(41,321)	(10,933)	(12,155)
Purchase of treasury stock	(55,095)	(58,671)	(91,250)
Settlement (prepayment) of accelerated share repurchase program		20,000	(8,750)
Cash dividends paid	(100,592)	(91,344)	(84,690)
Net cash provided by (used in) financing activities	346,363	(79,216)	337,750
Net increase (decrease) in cash and cash equivalents inclusive of restricted cash	308,940	185,379	(46,492)
Cash and cash equivalents inclusive of restricted cash at beginning of period	962,975	777,596	824,088
Cash and cash equivalents inclusive of restricted cash at end of period	$ 1,271,915	$ 962,975	$ 777,596