Leases - Components of lease expense, and lease assets and liabilities (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2021	Jun. 30, 2020	Jun. 30, 2021	Jun. 30, 2020	Dec. 31, 2020
Lease Cost:
Amortization of right-of-use assets (included in depreciation expense)	$ 202	$ 177	$ 396	$ 355
Interest on lease liabilities	83	109	175	227
Operating lease cost	3,802	3,997	7,596	8,138
Short-term lease cost	101	137	191	378
Variable lease cost	447	406	914	916
Total lease cost	4,635	$ 4,826	9,272	10,014
Cash paid for amounts included in the measurement of lease liabilities:
Operating cash flows used for finance lease			194	244
Operating cash flows used for operating leases			8,372	7,897
Financing cash flows used for finance lease			793	642
Right-of-use assets obtained in exchange for new operating lease liabilities			15,819	$ 4,504
Assets and Liabilities, Lessee [Abstract]
Finance lease right-of-use assets (included in other assets)	$ 2,052		$ 2,052		$ 2,448
Finance Lease, Right-of-Use Asset, Statement of Financial Position [Extensible List]	us-gaap:OtherAssetsMember		us-gaap:OtherAssetsMember		us-gaap:OtherAssetsMember
Operating lease right-of-use assets	$ 89,567		$ 89,567		$ 79,966
Finance lease liability, current (included in current installments of long-term debt)	$ 1,759		$ 1,759		$ 1,661
Finance Lease, Liability, Current, Statement of Financial Position [Extensible List]	bhe:LongTermDebtAndCapitalLeaseObligationsCurrentMember		bhe:LongTermDebtAndCapitalLeaseObligationsCurrentMember		bhe:LongTermDebtAndCapitalLeaseObligationsCurrentMember
Finance lease liability, noncurrent (included in long-term debt)	$ 1,940		$ 1,940		$ 2,832
Finance Lease, Liability, Noncurrent, Statement of Financial Position [Extensible List]	bhe:LongTermDebtAndCapitalLeaseObligationsMember		bhe:LongTermDebtAndCapitalLeaseObligationsMember		bhe:LongTermDebtAndCapitalLeaseObligationsMember
Operating lease liabilities, current (included in accrued liabilities)	$ 12,172		$ 12,172		$ 11,516
Operating Lease, Liability, Current, Statement of Financial Position [Extensible List]	us-gaap:AccruedLiabilitiesMember		us-gaap:AccruedLiabilitiesMember		us-gaap:AccruedLiabilitiesMember
Operating lease liabilities, noncurrent	$ 80,580		$ 80,580		$ 72,120
Weighted average remaining lease term – finance leases	2 years 6 months		2 years 6 months		3 years
Weighted average remaining lease term – operating leases	9 years 10 months 24 days		9 years 10 months 24 days		10 years
Weighted average discount rate – finance leases	9.00%		9.00%		9.00%
Weighted average discount rate – operating leases	4.20%		4.20%		4.40%