Balance Sheet Components - Other Accured Liabilities (Details) - USD ($) $ in Thousands	1 Months Ended	3 Months Ended	12 Months Ended
	Mar. 31, 2019	Mar. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Balance Sheet Components
Settlement accrued for reimbursement related claims			$ 1,378
Reserves for refunds to third-party payers	$ 11,051	$ 11,051	10,012
Accrued charges for outsourced testing	5,548	5,548	5,001
Testing and laboratory materials from suppliers	2,247	2,247	2,742
Marketing and corporate affairs	2,467	2,467	1,306
Legal, audit and consulting fees	1,471	1,471	1,058
Accrued shipping charges	564	564	852
Sales tax payable	1,442	1,442	1,255
Accrued specimen service fees	744	744	1,378
Accrued rent			903
Clinical trials and studies	1,841	1,841	1,694
Operating lease liabilities, current portion	5,147	5,147
Other accrued expenses	5,317	5,317	4,863
Total other accrued liabilities	37,839	37,839	32,442
Accrued settlement liability			1,400	$ 11,400
Additional reserves for refunds to insurance carriers		2,500
Settlement agreement installment paid	$ 1,400		$ 10,300
Revenue recognized		500
Overpayments from insurance carriers		$ 1,500