CONDENSED CONSOLIDATED STATEMENTS OF CASH FLOWS - USD ($) $ in Thousands	9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016
Cash flows from operating activities
Net loss	$ (83,988)	$ (79,250)
Adjustments to reconcile net loss to net cash provided by operating activities
Depreciation and amortization	24,263	20,000
Share-based compensation	62,805	56,337
Excess tax benefit from share-based award activity	0	(133)
Other	380	1,219
Changes in operating assets and liabilities:
Accounts receivable	(15,039)	(11,782)
Prepaid expenses and other current assets	(5,109)	(7,401)
Other assets and liabilities	(5,513)	(1,829)
Accounts payable	7,237	(2,220)
Accrued liabilities	6,843	2,645
Accrued compensation and related benefits	1,503	812
Deferred revenue	31,357	25,596
Net cash provided by operating activities	24,739	3,994
Cash flows from investing activities
Purchases of property and equipment	(13,334)	(12,494)
Internal-use software development costs	(5,237)	(4,313)
Purchases of marketable securities	(135,279)	(216,640)
Proceeds from maturities of marketable securities	88,960	23,971
Proceeds from sale of marketable securities	28,144	39,244
Cash paid for the acquisition of Outbound, net of cash acquired	(16,470)	0
Net cash used in investing activities	(53,216)	(170,232)
Cash flows from financing activities
Proceeds from exercise of employee stock options	18,550	19,886
Proceeds from employee stock purchase plan	10,980	8,704
Taxes paid related to net share settlement of share-based awards	(2,415)	(626)
Principal payment on debt	0	(323)
Excess tax benefit from share-based award activity	0	133
Net cash provided by financing activities	27,115	27,774
Effect of exchange rate changes on cash and cash equivalents	288	(173)
Net decrease in cash and cash equivalents	(1,074)	(138,637)
Cash and cash equivalents at beginning of period	93,677	216,226
Cash and cash equivalents at end of period	92,603	77,589
Supplemental cash flow data:
Cash paid for income taxes and interest	1,532	968
Non-cash investing and financing activities:
Share-based compensation capitalized in internal-use software development costs	1,984	1,761
Balance of property and equipment in accounts payable and accrued expenses	1,384	2,466
Property and equipment acquired through tenant improvement allowances	437	64
Vesting of early exercised stock options	$ 317	$ 509