Consolidated Statements of Cash Flows - USD ($)		12 Months Ended
		Dec. 31, 2018	Dec. 31, 2017		Dec. 31, 2016
Cash flows from operating activities:
Net income		$ 56,726,000	$ 48,888,000	[1],[2]	$ 61,733,000	[1],[2]
Adjustments to reconcile net income to net cash provided by operating activities:
Depreciation and amortization		48,719,000	38,984,000	[1]	34,580,000	[1]
Stock-based compensation expense		23,901,000	23,041,000	[1]	19,770,000	[1]
Unrealized gain on short term investments		(7,696,000)	0	[1]	0	[1]
Unrealized foreign exchange (gain)/loss, net		(8,620,000)	1,523,000	[1]	(1,001,000)	[1]
Deferred income tax (benefit)/expense		(625,000)	731,000	[1]	(3,384,000)	[1]
Impairment charges		20,056,000	0	[1],[2]	0	[1],[2]
Excess tax benefit from stock-based compensation		0	0	[1]	(4,326,000)	[1]
Change in fair value of earn-out consideration		0	0	[1]	(4,060,000)	[1]
Allowance for doubtful accounts receivable		(573,000)	2,816,000	[1]	0	[1]
Loss from equity-method investment		247,000	0	[1],[2]	0	[1],[2]
Others, net		903,000	252,000	[1]	(107,000)	[1]
Change in operating assets and liabilities, net of effects of acquisitions:
Accounts receivable		(10,046,000)	(20,482,000)	[1]	(18,062,000)	[1]
Prepaid expenses and other current assets		(4,509,000)	218,000	[1]	(5,421,000)	[1]
Accounts payable		(360,000)	1,706,000	[1]	(2,628,000)	[1]
Deferred revenue		(4,929,000)	(6,625,000)	[1]	5,726,000	[1]
Accrued employee costs		1,272,000	6,391,000	[1]	5,304,000	[1]
Accrued expenses and other liabilities		(1,084,000)	6,903,000	[1]	9,080,000	[1]
Advance income tax, net		(14,147,000)	11,037,000	[1]	437,000	[1]
Other assets		(6,800,000)	(2,224,000)	[1]	4,754,000	[1]
Net cash provided by operating activities	[1]	92,435,000	113,159,000		102,395,000
Cash flows from investing activities:
Purchase of property and equipment		(40,437,000)	(35,154,000)	[1]	(25,850,000)	[1]
Investment in equity affiliate		0	(3,000,000)	[1]	0	[1]
Business acquisition (net of cash acquired)		(231,829,000)	(23,300,000)	[1]	(28,666,000)	[1]
Purchase of investments		(133,434,000)	(402,721,000)	[1]	(182,471,000)	[1]
Proceeds from redemption of investments		128,208,000	241,439,000	[1]	182,320,000	[1]
Net cash used for investing activities		(277,492,000)	(222,736,000)	[1]	(54,667,000)	[1]
Cash flows from financing activities:
Principal payments on capital lease obligations		(152,000)	(174,000)	[1]	(348,000)	[1]
Proceeds from borrowings		246,614,000	60,574,000	[1]	0	[1]
Repayments of borrowings		(155,209,000)	(45,192,000)	[1]	(25,000,000)	[1]
Proceeds from convertible notes		149,000,000	0	[1]	0	[1]
Payment of debt issuance costs		(762,000)	(790,000)	[1]	0	[1]
Acquisition of treasury stock		(43,109,000)	(43,454,000)	[1]	(18,203,000)	[1]
Proceeds from exercise of stock options		1,397,000	8,561,000	[1]	6,499,000	[1]
Excess tax benefit from stock-based compensation		0	0	[1]	4,326,000	[1]
Net cash provided by/(used for) financing activities		197,779,000	(20,475,000)	[1]	(32,726,000)	[1]
Effect of exchange rate changes on cash, cash equivalents and restricted cash	[1]	(2,868,000)	3,935,000		(5,122,000)
Net increase/(decrease) in cash, cash equivalents and restricted cash(1)	[1]	9,854,000	(126,117,000)		9,880,000
Cash, cash equivalents and restricted cash - beginning of year	[1]	94,277,000	220,394,000		210,514,000
Cash, cash equivalents and restricted cash - end of year	[1]	104,131,000	94,277,000		220,394,000
Supplemental disclosure of cash flow information:
Restricted common stock issued for business acquisition		4,080,000	0	[1]	0	[1]
Cash paid for interest		4,725,000	1,122,000	[1]	1,178,000	[1]
Cash paid for taxes, net of refund		18,508,000	19,128,000	[1]	15,667,000	[1]
Assets acquired under capital lease		$ 277,000	$ 301,000	[1]	$ 334,000	[1]

[1] Adjusted pursuant to adoption of ASU 2016-18, Statements of Cash Flows, Restricted Cash. Refer to Note 8 and Note 27 to the consolidated financial statements.

[2] Adjusted pursuant to adoption of ASU No. 2017-07, Improving the Presentation of Net Periodic Pension Cost and Net Periodic Post-retirement Benefit Cost. Refer to Note 21 and Note 27 to the consolidated financial statements.