CONDENSED CONSOLIDATED STATEMENTS OF CASH FLOWS (Unaudited) - USD ($) $ in Thousands	9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018
Cash flows from operating activities:
Net income	$ 186,533	$ 180,291
Adjustments to reconcile net income to net cash provided by operating activities:
Depreciation and amortization expense	32,355	26,457
Operating lease right-of-use assets amortization expense	40,203	0
Bad debt expense	133	1,765
Deferred taxes	(3,105)	(36,372)
Stock-based compensation expense	53,024	46,736
Other	7,522	(3,434)
Changes in assets and liabilities:
Accounts receivable	(40,753)	(16,258)
Unbilled revenues	(37,080)	(41,544)
Prepaid expenses and other assets	237	(1,765)
Accounts payable	(1,844)	1,574
Accrued expenses and other liabilities	(3,092)	9,625
Operating lease liabilities	(39,230)	0
Due to employees	(5,627)	4,009
Taxes payable	(26,410)	(1,996)
Net cash provided by operating activities	162,866	169,088
Cash flows from investing activities:
Purchases of property and equipment	(52,295)	(27,465)
Acquisition of businesses, net of cash acquired (Note 2)	(28,655)	(50,264)
Other investing activities, net	(6,632)	(104)
Net cash used in investing activities	(87,582)	(77,833)
Cash flows from financing activities:
Proceeds from stock option exercises	28,798	32,007
Payments of withholding taxes related to net share settlements of restricted stock units	(14,521)	(7,068)
Repayment of debt	(7)	(3,485)
Acquisition of businesses, contingent consideration	(1,104)	0
Other financing activities, net	(19)	(603)
Net cash provided by financing activities	13,147	20,851
Effect of exchange rate changes on cash, cash equivalents and restricted cash	(5,753)	(8,660)
Net increase in cash, cash equivalents and restricted cash	82,678	103,446
Cash, cash equivalents and restricted cash, beginning of period	771,711	582,855
Cash, cash equivalents and restricted cash, end of period	$ 854,389	$ 686,301