CONDENSED CONSOLIDATED STATEMENTS OF CASH FLOWS (Unaudited) - USD ($) $ in Thousands	6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018
Cash flows from operating activities:
Net income	$ 119,531	$ 114,673
Adjustments to reconcile net income to net cash provided by operating activities:
Depreciation and amortization expense	21,228	17,138
Operating lease right-of-use assets amortization expense	25,732	0
Bad debt expense	167	1,529
Deferred taxes	(1,193)	(27,581)
Stock-based compensation expense	37,553	31,406
Other	3,938	(2,099)
Changes in assets and liabilities:
Accounts receivable	(44,582)	(15,051)
Unbilled revenues	(30,750)	(35,334)
Prepaid expenses and other assets	1,690	(4,495)
Accounts payable	(2,069)	1,008
Accrued expenses and other liabilities	(34,420)	(15,861)
Operating lease liabilities	(25,705)	0
Due to employees	(4,781)	1,351
Taxes payable	(22,512)	105
Net cash provided by operating activities	43,827	66,789
Cash flows from investing activities:
Purchases of property and equipment	(25,025)	(19,303)
Acquisition of businesses, net of cash acquired (Note 2)	(16,240)	(50,264)
Other investing activities, net	(6,180)	1,253
Net cash used in investing activities	(47,445)	(68,314)
Cash flows from financing activities:
Proceeds from stock option exercises	22,415	22,368
Payments of withholding taxes related to net share settlements of restricted stock units	(13,084)	(6,696)
Repayment of debt	(6)	(3,478)
Acquisition of businesses, contingent consideration	(1,104)	0
Other financing activities, net	(13)	(603)
Net cash provided by financing activities	8,208	11,591
Effect of exchange rate changes on cash, cash equivalents and restricted cash	2,248	(7,645)
Net increase in cash, cash equivalents and restricted cash	6,838	2,421
Cash, cash equivalents and restricted cash, beginning of period	771,711	582,855
Cash, cash equivalents and restricted cash, end of period	$ 778,549	$ 585,276