CONDENSED CONSOLIDATED STATEMENTS OF CASH FLOWS (UNAUDITED) - USD ($) $ in Thousands	6 Months Ended
	Jun. 30, 2022	Jun. 30, 2021
CASH FLOWS FROM OPERATING ACTIVITIES:
Net income	$ 110,671	$ 83,240
Adjustments to reconcile net income to net cash provided by operating activities:
Depreciation	8,977	7,763
Amortization	1,676	2,557
Stock-based compensation expense	10,025	6,441
Noncash lease expense	8,959	7,899
Deferred income tax (benefit) provision	(1,439)	2,667
Amortization and adjustment of deferred credit	(310)	(334)
Other	(323)	131
Changes in assets and liabilities:
Accounts receivable and unbilled, net	(39,059)	(353)
Prepaid expenses and other current assets	(18,789)	(14,889)
Accounts payable	2,552	(270)
Accrued expenses	15,643	11,937
Advanced billings	56,727	26,553
Lease liabilities	(7,705)	(7,956)
Other assets and liabilities, net	(4,730)	(5,306)
Net cash provided by operating activities	142,875	120,080
CASH FLOWS FROM INVESTING ACTIVITIES:
Property and equipment expenditures	(20,457)	(12,515)
Other	(1,878)	(3,133)
Net cash used in investing activities	(22,335)	(15,648)
CASH FLOWS FROM FINANCING ACTIVITIES:
Proceeds from stock option exercises	15,421	14,200
Repurchases of common stock	(800,667)	(55,877)
Proceeds from revolving loan	299,200
Payments on revolving loan	(49,500)
Net cash used in financing activities	(535,546)	(41,677)
EFFECT OF EXCHANGE RATES ON CASH, CASH EQUIVALENTS, AND RESTRICTED CASH	(3,747)	(1,512)
(DECREASE) INCREASE IN CASH, CASH EQUIVALENTS, AND RESTRICTED CASH	(418,753)	61,243
CASH, CASH EQUIVALENTS, AND RESTRICTED CASH — Beginning of period	461,304	277,766
CASH, CASH EQUIVALENTS, AND RESTRICTED CASH — End of period	42,551	339,009
SUPPLEMENTAL DISCLOSURE OF CASH FLOW INFORMATION—
Acquisition of property and equipment—non-cash	$ 7,441	$ 5,824