Borrowing Arrangements - Additional Information (Detail) £ in Thousands		1 Months Ended	3 Months Ended
	Mar. 04, 2019 USD ($)	Sep. 30, 2018	Mar. 31, 2019 USD ($)	Mar. 31, 2019 GBP (£)	Dec. 31, 2018 USD ($)
Line Of Credit Facility [Line Items]
Lessee lease term		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
Extended lease expiration date		2058-09
Lease repurchase percentage on lessor investment for properties		115.00%
Effective interest rate			6.00%	6.00%
Repayment of promissory notes and related accrued interest	$ 26,474,000
Revolving Credit and Security Agreement [Member]
Line Of Credit Facility [Line Items]
Initial term of credit facility			5 years
Agreement borrowing capacity			$ 100,000,000
Additional borrowing capacity			50,000,000
Long term debt			$ 40,037,000		$ 14,320,000
Interest on outstanding balance			2.22%
Line of credit, remaining borrowing capacity			$ 39,000,000
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
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 | £				£ 3,000
Revolving Credit and Security Agreement [Member] | Canadian Credit Facility [Member]
Line Of Credit Facility [Line Items]
Agreement borrowing capacity			$ 15,000,000