CONDENSED CONSOLIDATED STATEMENTS OF CASH FLOWS (UNAUDITED) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020
CASH FLOWS FROM OPERATING ACTIVITIES:
Net income	$ 43,306	$ 28,954
Adjustments to reconcile net income to net cash provided by operating activities:
Depreciation	3,812	2,453
Amortization	1,278	1,997
Stock-based compensation expense	2,871	5,445
Noncash lease expense	3,903	2,917
Deferred income tax provision	1,289	1,079
Amortization and adjustment of deferred credit	(167)	(181)
Other	124	(67)
Changes in assets and liabilities:
Accounts receivable and unbilled, net	1,089	19,301
Prepaid expenses and other current assets	(6,073)	(2,694)
Accounts payable	(2,638)	(6,809)
Accrued expenses	(10,043)	(1,757)
Advanced billings	22,143	(2,695)
Lease liabilities	(3,155)	(2,236)
Other assets and liabilities, net	(420)	3,441
Net cash provided by operating activities	57,319	49,148
CASH FLOWS FROM INVESTING ACTIVITIES:
Property and equipment expenditures	(6,507)	(5,561)
Other	(3,144)	39
Net cash used in investing activities	(9,651)	(5,522)
CASH FLOWS FROM FINANCING ACTIVITIES:
Proceeds from stock option exercises	9,102	1,331
Repurchases of common stock	0	(41,776)
Net cash provided by (used in) financing activities	9,102	(40,445)
EFFECT OF EXCHANGE RATES ON CASH, CASH EQUIVALENTS, AND RESTRICTED CASH	(1,659)	(1,102)
INCREASE IN CASH, CASH EQUIVALENTS, AND RESTRICTED CASH	55,111	2,079
CASH, CASH EQUIVALENTS, AND RESTRICTED CASH — Beginning of period	277,766	131,920
CASH, CASH EQUIVALENTS, AND RESTRICTED CASH — End of period	$ 332,877	$ 133,999