Summary of Significant Accounting Policies - Impact of New Accounting Standards ASC 606 on Balance Sheet (Details) - USD ($) $ in Thousands	Jun. 30, 2019	Mar. 31, 2019	Jan. 01, 2019	Dec. 31, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017
Assets
Accounts receivable	$ 51,671			$ 81,782
Inventory	74,066			50,997
Prepaid expenses and other current assets	4,915			3,755
Prepaid income taxes	419			390
Accounts receivable, net of current portion	1,181			2,388
Deferred tax assets	26,367			21,578
Other assets	2,780			3,293
Total assets	435,651			474,649
Liabilities:
Accrued expenses and other current liabilities	23,099			36,992
Deferred revenue	25,444			31,206
Deferred revenue, net of current portion	8,801			12,479
Total liabilities	366,038			399,793
Stockholders’ equity:
Accumulated deficit	(92,906)			(81,008)
Total stockholders’ equity	69,613	$ 65,434		74,856	$ 107,264	$ 71,833	$ 50,156
Total liabilities and stockholders’ equity	435,651			$ 474,649
Accounting Standards Update 2014-09
Assets
Accounts receivable			$ 81,629
Inventory			50,629
Prepaid expenses and other current assets			3,964
Accounts receivable, net of current portion			2,313
Deferred tax assets			20,986
Other assets			3,421
Total assets			473,798
Liabilities:
Accrued expenses and other current liabilities			38,037
Deferred revenue			29,016
Deferred revenue, net of current portion			10,623
Total liabilities			396,792
Stockholders’ equity:
Accumulated deficit			(78,858)
Total stockholders’ equity			77,006
Total liabilities and stockholders’ equity			473,798
Accounting Standards Update 2014-09 | Adjustments
Assets
Accounts receivable	130		(153)
Inventory	248		(368)
Prepaid expenses and other current assets	(138)		209
Prepaid income taxes	330
Accounts receivable, net of current portion	23		(75)
Deferred tax assets	402		(592)
Other assets	(78)		128
Total assets	917		(851)
Liabilities:
Accrued expenses and other current liabilities	(683)		1,045
Deferred revenue	2,374		(2,190)
Deferred revenue, net of current portion	1,856		(1,856)
Total liabilities	3,547		(3,001)
Stockholders’ equity:
Accumulated deficit	(2,630)		2,150
Total stockholders’ equity	(2,630)		2,150
Total liabilities and stockholders’ equity	917		$ (851)
Accounting Standards Update 2014-09 | Without adoption of ASC 606
Assets
Accounts receivable	51,801
Inventory	74,314
Prepaid expenses and other current assets	4,777
Prepaid income taxes	749
Accounts receivable, net of current portion	1,204
Deferred tax assets	26,769
Other assets	2,702
Total assets	436,568
Liabilities:
Accrued expenses and other current liabilities	22,416
Deferred revenue	27,818
Deferred revenue, net of current portion	10,657
Total liabilities	369,585
Stockholders’ equity:
Accumulated deficit	(95,536)
Total stockholders’ equity	66,983
Total liabilities and stockholders’ equity	$ 436,568