CONDENSED CONSOLIDATED STATEMENTS OF CASH FLOWS - USD ($) $ in Thousands	6 Months Ended
	Jun. 30, 2016	Jun. 30, 2015
Cash flows from operating activities
Net loss	$ (53,425)	$ (40,650)
Adjustments to reconcile net loss to net cash provided by (used in) operating activities:
Depreciation and amortization	13,147	8,804
Share-based compensation	36,341	23,614
Other	599	318
Excess tax benefit from share-based award activity	0	(95)
Changes in operating assets and liabilities:
Accounts receivable	(2,427)	(3,390)
Prepaid expenses and other current assets	(7,860)	(3,261)
Other assets and liabilities	(380)	(1,365)
Accounts payable	(579)	(1,063)
Accrued liabilities	1,803	1,270
Accrued compensation and related benefits	1,098	(2,259)
Deferred revenue	16,243	13,304
Net cash provided by (used in) operating activities	4,560	(4,773)
Cash flows from investing activities
Purchases of property and equipment	(8,410)	(7,406)
Internal-use software development costs	(2,773)	(2,383)
Purchases of marketable securities	(136,171)	(35,847)
Proceeds from maturities of marketable securities	16,476	18,020
Proceeds from sale of marketable securities	13,631	15,317
Cash paid for the acquisition of Zopim, net of cash acquired	0	(548)
Net cash used in investing activities	(117,247)	(12,847)
Cash flows from financing activities
Proceeds from follow-on public offering, net of issuance costs	0	190,110
Proceeds from exercise of employee stock options	9,387	4,976
Taxes paid related to net share settlement of equity awards	(345)	(203)
Proceeds from employee stock purchase plan	5,672	4,948
Excess tax benefit from share-based award activity	0	95
Principal payments on debt	(323)	(6,952)
Principal payments on capital lease obligations	0	(10)
Net cash provided by financing activities	14,391	192,964
Effect of exchange rate changes on cash and cash equivalents	106	60
Net (decrease) increase in cash and cash equivalents	(98,190)	175,404
Cash and cash equivalents at the beginning of period	216,226	80,265
Cash and cash equivalents at the end of period	118,036	255,669
Supplemental cash flow data:
Cash paid for interest and income taxes	437	617
Non-cash investing and financing activities:
Balance of property and equipment in accounts payable and accrued expenses	1,552	962
Share-based compensation capitalized in internal-use software development costs	1,075	1,262
Vesting of early exercised stock options	374	576
Property and equipment acquired through tenant improvement allowances	$ 0	$ 174