CONDENSED CONSOLIDATED STATEMENTS OF CASH FLOWS (Unaudited) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2016	Mar. 31, 2015
Cash flows from operating activities
Net loss	$ (27,171)	$ (19,168)
Adjustments to reconcile net loss to net cash provided by (used in) operating activities:
Depreciation and amortization	6,526	4,223
Share-based compensation	17,695	10,229
Other	403	172
Changes in operating assets and liabilities:
Accounts receivable	1,898	(635)
Prepaid expenses and other current assets	862	(793)
Other assets and liabilities	(383)	(638)
Accounts payable	(1,851)	(1,012)
Accrued liabilities	2,307	1,323
Accrued compensation and related benefits	(2,066)	(2,837)
Deferred revenue	6,369	3,941
Net cash provided by (used in) operating activities	4,589	(5,195)
Cash flows from investing activities
Purchases of property and equipment	(3,249)	(3,356)
Internal-use software development costs	(1,351)	(1,317)
Purchases of marketable securities	(20,795)	(14,801)
Proceeds from maturities of marketable securities	10,051	7,520
Proceeds from sale of marketable securities	7,604	6,141
Cash paid for the acquisition of Zopim, net of cash acquired		(548)
Net cash used in investing activities	(7,740)	(6,361)
Cash flows from financing activities
Proceeds from follow-on public offering, net of issuance costs		190,794
Proceeds from exercise of employee stock options	1,915	2,938
Taxes paid related to net share settlement of equity awards	(189)	(82)
Proceeds from employee stock purchase plan	3,144	2,468
Principal payments on debt		(753)
Principal payments on capital lease obligations		(10)
Net cash provided by financing activities	4,870	195,355
Effect of exchange rate changes on cash and cash equivalents	(154)	158
Net increase in cash and cash equivalents	1,565	183,957
Cash and cash equivalents at the beginning of period	216,226	80,265
Cash and cash equivalents at the end of period	217,791	264,222
Supplemental cash flow data:
Cash paid for interest and income taxes	168	122
Non-cash investing and financing activities:
Balance of property and equipment in accounts payable and accrued expenses	2,345	497
Share-based compensation capitalized in internal-use software development costs	563	545
Vesting of early exercised stock options	$ 232	311
Property and equipment acquired through tenant improvement allowances		174
Follow-on offering related costs not yet paid for		$ 605