CONSOLIDATED STATEMENTS OF CASH FLOWS - USD ($) $ in Thousands	6 Months Ended
	Jun. 30, 2017	Jun. 30, 2016
Cash flows used in operating activities:
Net loss	$ (31,069)	$ (30,183)
Adjustments to reconcile net loss to net cash used in operating activities:
Depreciation and amortization	5,275	3,066
Allowance for doubtful accounts	764	1,429
Stock-based compensation	7,662	2,922
Deferred income taxes	299	172
Accretion of interest	28	175
Changes in operating assets and liabilities:
Accounts receivable	(1,186)	(2,504)
Prepaid expenses and other current assets	700	435
Other assets	107	(12)
Accounts payable	(1,085)	(1,707)
Accrued expenses and other current liabilities	1,703	(1,648)
Accrued compensation	(264)	(1,695)
Other liabilities	1,645	616
Net cash used in operating activities	(15,421)	(28,934)
Cash flows (used in) provided by investing activities:
Purchase of property and equipment	(1,299)	(778)
Purchase of internal-use software	(285)	(658)
Purchase of marketable securities	(34,954)	(44,188)
Proceeds from marketable securities	19,677	69,749
Net cash (used in) provided by investing activities	(16,861)	24,125
Cash flows provided by financing activities:
Net proceeds from the exercise of stock options	4,316	590
Proceeds from issuance of convertible notes	263,722
Proceeds from borrowing under bank and other debt		5,500
Repayment of bank loan and other debt	(2,000)	(625)
Proceeds from issuance of common stock	123,928
Proceeds from employee stock purchase plan	1,265
Cash for withholding taxes on stock-based awards, net	260	59
Net cash provided by financing activities	391,491	5,524
Net increase in cash and cash equivalents	359,209	715
Cash and cash equivalents at beginning of the period	50,015	55,066
Cash and cash equivalents at end of the period	409,224	55,781
Interest paid	$ 1,847	$ 1,050