CONSOLIDATED STATEMENTS OF CASH FLOWS - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
CASH FLOWS FROM OPERATING ACTIVITIES:
Net income	$ 181,848	$ 145,384	$ 100,443
Adjustments to reconcile net income to net cash provided by operating activities:
Depreciation	16,005	11,652	8,360
Amortization	5,114	7,876	14,829
Stock-based compensation expense	14,469	13,784	20,741
Amortization of debt issuance costs and discount	0	0	954
Noncash lease expense	16,288	13,924	9,949
Deferred income tax (benefit) provision	(37,112)	527	10,050
Amortization and adjustment of deferred credit	(668)	(706)	(801)
Other	676	(22)	1,754
Changes in assets and liabilities:
Accounts receivable and unbilled, net	(24,982)	(5,530)	(21,256)
Prepaid expenses and other current assets	(9,134)	(3,724)	(7,381)
Accounts payable	1,866	(2,597)	4,730
Accrued expenses	26,156	24,231	21,824
Advanced billings	88,977	63,407	44,584
Lease liabilities	(15,632)	(11,506)	(9,034)
Other assets and liabilities, net	(544)	1,976	2,121
Net cash provided by operating activities	263,327	258,676	201,867
CASH FLOWS FROM INVESTING ACTIVITIES:
Property and equipment expenditures	(28,271)	(31,340)	(17,912)
Other	(3,093)	126	(1,232)
Net cash used in investing activities	(31,364)	(31,214)	(19,144)
CASH FLOWS FROM FINANCING ACTIVITIES:
Proceeds from stock option exercises	17,643	15,992	6,520
Repurchases of common stock	(62,096)	(98,274)	0
Payment of debt	0	0	(80,438)
Net cash used in financing activities	(44,453)	(82,282)	(73,918)
EFFECT OF EXCHANGE RATES ON CASH, CASH EQUIVALENTS, AND RESTRICTED CASH	(3,972)	666	(167)
INCREASE IN CASH, CASH EQUIVALENTS, AND RESTRICTED CASH	183,538	145,846	108,638
CASH, CASH EQUIVALENTS, AND RESTRICTED CASH — Beginning of period	277,766	131,920	23,282
CASH, CASH EQUIVALENTS, AND RESTRICTED CASH — End of period	461,304	277,766	131,920
SUPPLEMENTAL DISCLOSURE OF CASH FLOW INFORMATION—
Cash paid during the period for income taxes	56,243	23,105	13,235
Cash paid during the period for interest	123	104	1,489
Acquisition of property and equipment—non-cash	$ 6,352	$ 18,980	$ 2,529