Unaudited Consolidated Statements of Cash Flows - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2017	Mar. 31, 2016
Cash flows from operating activities
Net loss	$ (20,996)	$ (7,847)
Adjustments to reconcile net loss to net cash flows used in operating activities:
Amortization of lease incentive obligation	(17)
Depreciation of property and equipment	315	153
Share-based compensation expense	2,999	866
Deferred rent	1,031	136
Deferred income taxes		(5)
Changes in operating assets and liabilities:
Prepaid expenses and other current assets	(1,813)	(414)
Other non-current assets		(53)
Accounts payable	1,017	(296)
Accrued expenses and other current liabilities	(537)	329
Deferred revenue	(676)
Other non-current liabilities	1,259	(5)
Net cash used in operating activities	(17,418)	(7,136)
Cash flows from investing activities
Increase in restricted cash	(3)
Purchases of property and equipment	(3,635)	(685)
Net cash used in investing activities	(3,638)	(685)
Cash flows from financing activities
Payments on capital lease obligation	(16)	(16)
Proceeds from the exercise of share options	206
Net cash provided by (used in) financing activities	190	(16)
Effect of foreign exchange rates on cash	57	14
Net increase (decrease) in cash and cash equivalents	(20,809)	(7,823)
Cash and cash equivalents at beginning of period	150,293	161,220
Cash and cash equivalents at end of period	129,484	153,397
Supplemental disclosure of cash flow information:
Increase in the lease incentive obligation during the period	1,082
Property and equipment purchases in accounts payable and accrued expenses at period end	$ 2,976	$ 185