Consolidated Statements of Cash Flows (Unaudited) - USD ($) $ in Thousands	9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017
Cash flows from operating activities:
Net income	$ 52,869	$ 58,243
Adjustments to reconcile net income to net cash provided by operating activities:
Depreciation and amortization	35,345	28,771
Stock-based compensation expense	17,311	16,771
Unrealized gain on short term investments	(5,423)	(4,437)
Unrealized foreign exchange (gain)/loss, net	(14,375)	446
Deferred income tax benefit	(986)	(5,417)
Allowances for doubtful accounts receivable	(620)	2,706
Loss from equity-method investment	176	0
Others, net	193	12
Change in operating assets and liabilities:
Accounts receivable	(9,354)	(22,064)
Prepaid expenses and other current assets	(3,344)	5,194
Accounts payable	(1,414)	371
Deferred revenue	(5,199)	(8,155)
Accrued employee costs	(7,680)	(915)
Accrued expenses and other liabilities	(436)	267
Advance income tax, net	(4,228)	(2,607)
Other assets	(5,984)	1,241
Net cash provided by operating activities	46,851	70,427
Cash flows from investing activities:
Purchase of property and equipment	(30,070)	(26,759)
Business acquisition (net of cash acquired)	(231,918)	(724)
Purchase of investments	(57,957)	(197,897)
Proceeds from redemption of investments	79,536	54,238
Net cash used for investing activities	(240,409)	(171,142)
Cash flows from financing activities:
Principal payments on capital lease obligations	(105)	(133)
Proceeds from borrowings	245,000	0
Repayments of borrowings	(5,083)	0
Acquisition of treasury stock	(32,793)	(32,336)
Proceeds from exercise of stock options	1,084	4,276
Net cash provided by/(used for) financing activities	208,103	(28,193)
Effect of exchange rate changes on cash, cash equivalents and restricted cash	(3,008)	1,802
Net increase/(decrease) in cash, cash equivalents, and restricted cash	11,537	(127,106)
Cash, cash equivalents, and restricted cash at beginning of period	94,277	220,394
Cash, cash equivalents, and restricted cash at end of period	$ 105,814	$ 93,288