CONSOLIDATED STATEMENTS OF CASH FLOWS $ in Thousands	12 Months Ended
	Dec. 31, 2019 USD ($)	Dec. 31, 2018 USD ($)	Dec. 31, 2017 USD ($)
Cash flows from operating activities:
Net income	$ 261,057	$ 240,256	$ 72,760
Adjustments to reconcile net income to net cash provided by operating activities:
Depreciation and amortization expense	45,317	36,640	28,562
Operating lease right-of-use assets amortization expense	55,859	0	0
Bad debt expense	1,619	848	51
Deferred taxes	(7,764)	(48,000)	12,561
Stock-based compensation expense	72,036	59,188	52,407
Other	4,764	(1,712)	(4,010)
Changes in assets and liabilities:
Trade receivables and contract assets	(87,174)	(46,902)	(81,488)
Prepaid and other assets	(7,155)	(8,432)	1,061
Accounts payable	(1,685)	(772)	1,221
Accrued expenses and other liabilities	27,125	51,953	47,803
Operating lease liabilities	(53,419)	0	0
Income taxes payable	(23,127)	9,151	61,892
Net cash provided by operating activities	287,453	292,218	192,820
Cash flows from investing activities:
Purchases of property and equipment	(99,308)	(37,574)	(29,806)
Decrease in time deposits, net	0	418	0
Acquisition of businesses, net of cash acquired (Note 2)	(39,322)	(74,268)	(6,810)
Other investing activities, net	(6,739)	(699)	465
Net cash used in investing activities	(145,369)	(112,123)	(36,151)
Cash flows from financing activities:
Proceeds from stock option exercises	37,003	34,845	53,984
Payments of withholding taxes related to net share settlements of restricted stock units	(15,503)	(7,747)	(3,194)
Proceeds from debt (Note 8)	0	0	25,000
Repayment of debt (Note 8)	(9)	(3,494)	(25,103)
Acquisition of businesses, contingent consideration	(1,104)	0	0
Other financing activities, net	(24)	(603)	(941)
Net cash provided by financing activities	20,363	23,001	49,746
Effect of exchange rate changes on cash, cash equivalents and restricted cash	3,530	(14,240)	11,776
Net increase in cash, cash equivalents and restricted cash	165,977	188,856	218,191
Cash, cash equivalents and restricted cash, beginning of period	771,711	582,855	364,664
Cash, cash equivalents and restricted cash, end of period	937,688	771,711	582,855
Cash paid during the year for:
Income taxes, net of refunds	65,306	40,437	26,669
Interest	832	777	548
Supplemental disclosure of non-cash investing and financing activities
Acquisition-date fair value of contingent consideration issued for acquisition of businesses	3,876	8,390	0
Capital expenditures incurred but not yet paid	$ 16,921	$ 2,140	$ 1,042