CONSOLIDATED STATEMENTS OF CASH FLOWS - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Cash flows from operating activities
Net loss	$ (26,141)	$ (29,309)	$ (32,099)
Adjustments to reconcile net loss to net cash provided by operating activities
Depreciation and amortization	16,214	14,663	13,467
Share-based compensation	42,060	30,840	22,088
Foreign currency remeasurement (gain) loss	(666)	2,615	843
Tax benefit from release of valuation allowance			(1,411)
Impairment of fixed assets			1,317
Non-cash interest and other expense related to debt			156
Net accretion of discount and amortization of premium on available-for-sale securities			616
Provision for bad debt	1,674	648	411
Deferred income tax	(47)	(36)	(8)
Others	181	583	416
Changes in assets and liabilities
Accounts receivable	(16,770)	(11,728)	(11,923)
Prepaid expenses and other current assets	(6,199)	(1,018)	(4,242)
Other assets	1,533	76	(422)
Accounts payable	176	1,516	1,591
Accrued liabilities	9,918	15,165	2,354
Deferred revenue	19,256	8,502	11,071
Other liabilities	(24)	(2,809)	861
Net cash provided by operating activities	41,165	29,708	5,086
Cash flows from investing activities
Purchases of property and equipment	(19,497)	(14,236)	(14,631)
Capitalized internal-use software	(7,420)	(2,162)	(2,513)
Cash paid for business combination, net of cash acquired			(4,670)
Restricted investments	530		100
Proceeds from the maturity of available-for-sale securities			28,080
Net cash (used in) provided by investing activities	(26,387)	(16,398)	6,366
Cash flows from financing activities
Proceeds from issuance of stock in connection with stock plans	25,495	15,104	19,524
Payment of holdback from Glip acquisition		(1,500)
Repayment of debt	(14,840)	(3,750)	(6,142)
Repayment of capital lease obligations	(181)	(269)	(594)
Taxes paid related to net share settlement of equity awards	(3,691)	(255)	(151)
Net cash provided by financing activities	6,783	9,330	12,637
Effect of exchange rate changes on cash and cash equivalents	(724)	127	317
Net increase in cash and cash equivalents	20,837	22,767	24,406
Cash and cash equivalents
Beginning of period	160,355	137,588	113,182
End of period	181,192	160,355	137,588
Supplemental disclosure of cash flow data
Cash paid for interest	116	711	1,893
Cash paid for income taxes	216	229	100
Non-cash investing and financing activities
Issuance of common stock for business combination			3,447
Change in liability for unvested exercised options		3	38
Equipment and capitalized internal-use software purchased and unpaid at period end	1,699	2,152	719
Change in unrealized gain on available-for-sale securities			$ 217
Glip, Inc.
Non-cash investing and financing activities
Issuance of common stock for business combination	$ 3,560	$ 1,080