CONDENSED CONSOLIDATED STATEMENTS OF CASH FLOWS (UNAUDITED) - USD ($) $ in Thousands	9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019
Cash flows from operating activities:
Net income	$ 383,163	$ 321,995
Adjustments to reconcile net income to net cash provided by operating activities:
Amortization	80,190	78,418
Depreciation	18,836	17,516
Non-cash stock-based compensation	43,465	34,679
Change in estimated acquisition earn-out payables	4,996	(6,920)
Deferred income taxes	4,598	6,172
Amortization of debt discount and disposal of deferred financing costs	1,619	1,521
Amortization (accretion) of discounts and premiums, investment	26	(11)
Net (gain)/loss on sales of investments, fixed assets and customer accounts	(720)	(4,108)
Payments on acquisition earn-outs in excess of original estimated payables	(1,199)	(351)
Changes in operating assets and liabilities, net of effect from acquisitions and divestitures:
Premiums, commissions and fees receivable (increase) decrease	(63,124)	(41,078)
Reinsurance recoverables (increase) decrease	(48,959)	(244,391)
Prepaid reinsurance premiums (increase) decrease	(31,594)	(45,645)
Other assets (increase) decrease	4,071	(23,105)
Premiums payable to insurance companies increase (decrease)	58,986	43,055
Premium deposits and credits due customers increase (decrease)	1,823	12,335
Losses and loss adjustment reserve increase (decrease)	48,959	244,575
Unearned premiums increase (decrease)	31,594	45,645
Accounts payable increase (decrease)	53,041	22,086
Accrued expenses and other liabilities increase (decrease)	(22,458)	(22,462)
Other liabilities increase (decrease)	(27,725)	7,194
Net cash provided by operating activities	539,588	447,120
Cash flows from investing activities:
Additions to fixed assets	(55,820)	(47,358)
Payments for businesses acquired, net of cash acquired	(402,358)	(288,393)
Proceeds from sales of fixed assets and customer accounts	8,622	3,499
Purchases of investments	(10,129)	(15,769)
Proceeds from sales of investments	7,434	8,385
Net cash used in investing activities	(452,251)	(339,636)
Cash flows from financing activities:
Payments on acquisition earn-outs	(9,859)	(7,514)
Proceeds from long-term debt	700,000	350,000
Payments on long-term debt	(41,250)	(36,250)
Deferred debt issuance costs	(6,788)	(3,701)
Borrowings on revolving credit facility	250,000	100,000
Payments on revolving credit facilities	(350,000)	(350,000)
Issuances of common stock for employee stock benefit plans	29,940	24,948
Repurchase shares to fund tax withholdings for non-cash stock-based compensation	(41,126)	(10,794)
Purchase of treasury stock	(7,313)	(29,742)
Settlement (prepayment) of accelerated share repurchase program		20,000
Cash dividends paid	(72,075)	(67,432)
Net cash provided by (used in) financing activities	451,529	(10,485)
Net increase in cash and cash equivalents inclusive of restricted cash	538,866	96,999
Cash and cash equivalents inclusive of restricted cash at beginning of period	962,975	777,596
Cash and cash equivalents inclusive of restricted cash at end of period	$ 1,501,841	$ 874,595