Consolidated Statements of Cash Flows - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Cash flows from operating activities:
Net income	$ 67,659	$ 56,726	$ 48,888
Adjustments to reconcile net income to net cash provided by operating activities:
Depreciation and amortization expense	52,193	48,719	38,984
Stock-based compensation expense	26,070	23,901	23,041
Amortization of operating lease right-of-use assets	27,335	0	0
Unrealized gain on short term investments	(10,116)	(7,696)	0
Unrealized foreign exchange (gain)/loss, net	(321)	(8,620)	1,523
Deferred income tax (benefit)/expense	(12,345)	(625)	731
Allowance for doubtful accounts receivable	614	(573)	2,816
Loss from equity-method investment	269	247	0
Amortization of non-cash interest expense related to convertible senior notes	2,472	0	0
Impairment charges	3,627	20,056	0
Others, net	(1,205)	903	252
Change in operating assets and liabilities, net of effects of acquisitions:
Accounts receivable	(7,093)	(10,046)	(20,482)
Prepaid expenses and other current assets	1,215	(4,509)	218
Advance income tax, net	7,194	(14,147)	11,037
Other assets	(2,204)	(6,800)	(2,224)
Accounts payable	134	(360)	1,706
Deferred revenue	6,679	(4,929)	(6,625)
Accrued employee costs	16,915	1,272	6,391
Accrued expenses and other liabilities	14,141	(1,084)	6,903
Operating lease liabilities	(24,813)	0	0
Net cash provided by operating activities	168,420	92,435	113,159
Cash flows from investing activities:
Purchases of property and equipment	(40,138)	(40,437)	(35,154)
Investment in equity affiliate	0	0	(3,000)
Purchase of non-controlling interest	(241)	0	0
Business acquisition (net of cash acquired)	0	(231,829)	(23,300)
Purchase of investments	(187,974)	(133,434)	(402,721)
Proceeds from redemption of investments	176,968	128,208	241,439
Net cash used for investing activities	(51,385)	(277,492)	(222,736)
Cash flows from financing activities:
Principal payments of finance lease liabilities	(336)	(152)	(174)
Proceeds from borrowings	46,000	246,614	60,574
Repayments of borrowings	(98,247)	(155,209)	(45,192)
Proceeds from convertible notes	0	149,000	0
Payment of debt issuance costs	(117)	(762)	(790)
Acquisition of treasury stock	(41,364)	(43,109)	(43,454)
Proceeds from exercise of stock options	987	1,397	8,561
Net cash (used for)/provided by financing activities	(93,077)	197,779	(20,475)
Effect of exchange rate changes on cash, cash equivalents and restricted cash	(1,045)	(2,868)	3,935
Net increase/(decrease) in cash, cash equivalents and restricted cash	22,913	9,854	(126,117)
Cash, cash equivalents and restricted cash at the beginning of the period	104,131	94,277	220,394
Cash, cash equivalents and restricted cash at the end of the period	127,044	104,131	94,277
Supplemental disclosure of cash flow information:
Restricted common stock issued for business acquisition	0	4,080	0
Cash paid for interest	10,649	4,725	1,122
Cash paid for taxes, net of refund	19,087	18,508	19,128
Assets acquired under finance lease	$ 506	$ 277	$ 301