CONDENSED CONSOLIDATED STATEMENTS OF CASH FLOWS (UNAUDITED) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2022	Mar. 31, 2021
CASH FLOWS FROM OPERATING ACTIVITIES:
Net income	$ 61,311	$ 43,306
Adjustments to reconcile net income to net cash provided by operating activities:
Depreciation	4,270	3,812
Amortization	838	1,278
Stock-based compensation expense	4,372	2,871
Noncash lease expense	4,537	3,903
Deferred income tax (benefit) provision	(713)	1,289
Amortization and adjustment of deferred credit	(155)	(167)
Other	(265)	124
Changes in assets and liabilities:
Accounts receivable and unbilled, net	(38,224)	1,089
Prepaid expenses and other current assets	(5,547)	(6,073)
Accounts payable	(1,041)	(2,638)
Accrued expenses	(3,651)	(10,043)
Advanced billings	22,580	22,143
Lease liabilities	(3,542)	(3,155)
Other assets and liabilities, net	1,486	(420)
Net cash provided by operating activities	46,256	57,319
CASH FLOWS FROM INVESTING ACTIVITIES:
Property and equipment expenditures	(9,257)	(6,507)
Other	(1,951)	(3,144)
Net cash used in investing activities	(11,208)	(9,651)
CASH FLOWS FROM FINANCING ACTIVITIES:
Proceeds from stock option exercises	13,867	9,102
Repurchases of common stock	(425,950)
Proceeds from revolving loan	49,500
Payments on revolving loan	(49,500)
Net cash (used in) provided by financing activities	(412,083)	9,102
EFFECT OF EXCHANGE RATES ON CASH, CASH EQUIVALENTS, AND RESTRICTED CASH	(1,426)	(1,659)
(DECREASE) INCREASE IN CASH, CASH EQUIVALENTS, AND RESTRICTED CASH	(378,461)	55,111
CASH, CASH EQUIVALENTS, AND RESTRICTED CASH — Beginning of period	461,304	277,766
CASH, CASH EQUIVALENTS, AND RESTRICTED CASH — End of period	82,843	332,877
SUPPLEMENTAL DISCLOSURE OF CASH FLOW INFORMATION—
Acquisition of property and equipment—non-cash	$ 7,375	$ 6,531