CONDENSED CONSOLIDATED STATEMENTS OF CASH FLOWS (Unaudited) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018
Cash flows from operating activities:
Net income	$ 60,754	$ 64,418
Adjustments to reconcile net income to net cash (used in)/provided by operating activities:
Depreciation and amortization expense	10,200	8,176
Operating lease right-of-use assets amortization expense	12,187	0
Bad debt recovery	(133)
Bad debt expense		199
Deferred taxes	846	(23,290)
Stock-based compensation expense	21,856	16,596
Other	520	(1,982)
Changes in assets and liabilities:
Accounts receivable	(8,820)	12,475
Unbilled revenues	(39,523)	(48,193)
Prepaid expenses and other assets	401	(7,623)
Accounts payable	(2,488)	2,520
Accrued expenses and other liabilities	(51,079)	(31,470)
Operating lease liabilities	(13,175)	0
Due to employees	24,297	11,656
Taxes payable	(16,045)	3,848
Net cash (used in)/provided by operating activities	(202)	7,330
Cash flows from investing activities:
Purchases of property and equipment	(13,424)	(10,711)
Acquisition of businesses, net of cash acquired (Note 2)	0	(50,264)
Other investing activities, net	(5,136)	811
Net cash used in investing activities	(18,560)	(60,164)
Cash flows from financing activities:
Proceeds from stock option exercises	11,402	7,588
Payments of withholding taxes related to net share settlements of restricted stock units	(1,208)	(106)
Repayment of debt	(4)	(3,466)
Other financing activities, net	(9)	0
Net cash provided by financing activities	10,181	4,016
Effect of exchange rate changes on cash, cash equivalents and restricted cash	548	3,040
Net decrease in cash, cash equivalents and restricted cash	(8,033)	(45,778)
Cash, cash equivalents and restricted cash, beginning of period	771,711	582,855
Cash, cash equivalents and restricted cash, end of period	$ 763,678	$ 537,077