Leases - Supplemental Balance Sheet Information Related to Operating and Finance Leases (Details) - USD ($) $ in Thousands	Dec. 31, 2019	Dec. 31, 2018
Assets And Liabilities Lessee [Abstract]
Operating lease right-of-use assets	$ 7,494
Operating Lease, Right-of-Use Asset, Statement of Financial Position [Extensible List]	us-gaap:OtherAssetsMember
Finance lease right-of-use assets	$ 78
Finance Lease, Right-of-Use Asset, Statement of Financial Position [Extensible List]	us-gaap:OtherAssetsMember
Total right-of use assets	$ 7,572
Operating lease liabilities	$ 1,259
Operating Lease, Liability, Current, Statement of Financial Position [Extensible List]	sien:AccruedAndOtherCurrentLiabilitiesMember	sien:AccruedAndOtherCurrentLiabilitiesMember
Finance lease liabilities	$ 40
Finance Lease, Liability, Current, Statement of Financial Position [Extensible List]	sien:AccruedAndOtherCurrentLiabilitiesMember	sien:AccruedAndOtherCurrentLiabilitiesMember
Operating lease liabilities	$ 6,434
Operating Lease, Liability, Noncurrent, Statement of Financial Position [Extensible List]	sien:WarrantyReserveAndOtherLongTermLiabilitiesMember
Finance lease liabilities	$ 35
Finance Lease, Liability, Noncurrent, Statement of Financial Position [Extensible List]	sien:WarrantyReserveAndOtherLongTermLiabilitiesMember
Total lease liabilities	$ 7,768
Weighted average remaining lease term (years)
Operating leases	5 years
Finance leases	2 years
Weighted average discount rate
Operating leases	7.45%
Finance leases	4.06%