Borrowing Arrangements - Additional Information (Detail) £ in Thousands		1 Months Ended	9 Months Ended
	May 20, 2016 USD ($)	Sep. 30, 2018 USD ($)	Sep. 30, 2018 USD ($)	Sep. 30, 2017 USD ($)	Sep. 30, 2018 GBP (£)	Dec. 31, 2017 USD ($)
Line Of Credit Facility [Line Items]
Lessee lease term		20 years	20 years		20 years
Lessee, operating lease, option to extend		UES may extend the lease for four successive periods of approximately five years each. If fully extended, the lease would expire in September 2058.
Lessee, operating term period		5 years	5 years		5 years
Extended lease expiration date		2058-09
Lease repurchase percentage on lessor investment for properties		115.00%
Gross proceeds from sale-leaseback finacing transaction		$ 19,000,000	$ 19,000,000	$ 0
Initial annual payment due		1,644,000	1,644,000
Deferred financing fees		$ 477,000	$ 477,000	$ 0
Amortization period for defferred financing fee		7 years
Maximum [Member]
Line Of Credit Facility [Line Items]
Incremental percentage on annual lease payment		2.00%
Change in consumer price index percentage		1.25%
Revolving Credit and Security Agreement [Member]
Line Of Credit Facility [Line Items]
Initial term of credit facility	5 years
Line of credit facility maturity date	May 31, 2021
Agreement borrowing capacity	$ 100,000,000
Additional borrowing capacity	$ 50,000,000
Line of credit facility interest annual increase rate			0.50%
Long term debt		$ 13,803,000	$ 13,803,000			$ 20,349,000
Line of credit, remaining borrowing capacity		$ 45,000,000	$ 45,000,000
Average interest rate			2.77%
Revolving Credit and Security Agreement [Member] | Minimum [Member]
Line Of Credit Facility [Line Items]
Commitment fee payable percentage	0.25%
Revolving Credit and Security Agreement [Member] | Maximum [Member]
Line Of Credit Facility [Line Items]
Commitment fee payable percentage	0.375%
Fixed charge coverage ratio		1.00	1.00		1.00
Revolving Credit and Security Agreement [Member] | London Interbank Offered Rate (LIBOR) [Member]
Line Of Credit Facility [Line Items]
Debt instrument description of interest rate			LIBOR plus an applicable margin ranging between 1.75% to 2.25%
Revolving Credit and Security Agreement [Member] | London Interbank Offered Rate (LIBOR) [Member] | Minimum [Member]
Line Of Credit Facility [Line Items]
Debt instrument basis spread	1.75%
Revolving Credit and Security Agreement [Member] | London Interbank Offered Rate (LIBOR) [Member] | Maximum [Member]
Line Of Credit Facility [Line Items]
Debt instrument basis spread	2.25%
Revolving Credit and Security Agreement [Member] | Base Rate [Member]
Line Of Credit Facility [Line Items]
Debt instrument description of interest rate			the base rate plus an applicable margin ranging between 0.75% to 1.25%
Revolving Credit and Security Agreement [Member] | Base Rate [Member] | Minimum [Member]
Line Of Credit Facility [Line Items]
Debt instrument basis spread	0.75%
Revolving Credit and Security Agreement [Member] | Base Rate [Member] | Maximum [Member]
Line Of Credit Facility [Line Items]
Debt instrument basis spread	1.25%
Revolving Credit and Security Agreement [Member] | Letter of Credit [Member]
Line Of Credit Facility [Line Items]
Agreement borrowing capacity	$ 40,000,000
Revolving Credit and Security Agreement [Member] | European Credit Facility [Member]
Line Of Credit Facility [Line Items]
Agreement borrowing capacity	15,000,000
Long term debt | £					£ 1,000
Revolving Credit and Security Agreement [Member] | Canadian Credit Facility [Member]
Line Of Credit Facility [Line Items]
Agreement borrowing capacity	$ 15,000,000