The Company adopted ASU 2016-02 standard on a prospective basis on January 1, 2019 and used the effective date as the date of initial application. Therefore, prior period financial information has not been adjusted and continues to be reflected in accordance with the Company’s historical accounting policy. The standard establishes a right-of-use (ROU) model that requires a lessee to recognize a ROU asset and lease liability on the balance sheet for all leases with a term longer than 12 months.

The Company elected to adopt the "package of practical expedients" under ASU No. 2018-11, which allows the Company to carry forward its historical assessments of whether existing agreements contain a lease, classification of existing lease agreements, and treatment of initial direct lease costs. The Company also elected to exclude short-term leases (those with terms of 12 months or less) from the balance sheet presentation and accounts for non-lease and lease components as a single lease component for all asset classes.

The Company determines if an arrangement is a lease at inception. All of the Company’s leases are operating leases and are included in ROU assets, accounts payable and operating lease liabilities in the Company's Condensed Consolidated Balance Sheet at June 30, 2019.

ROU assets represent the Company’s right to use an underlying asset for the lease term and lease liabilities represent the Company’s obligations to make lease payments arising from the lease. Operating lease ROU assets and liabilities are recognized at commencement date based on the present value of lease payments over the lease term. The Company uses its incremental borrowing rate based on the information available at commencement date in determining the present value of lease payments. The Company’s lease terms may include options to extend or terminate the lease. The lease term includes options to extend when we are reasonably certain to exercise the option. We are not, however, reasonably certain that we will exercise any of the options to extend and as such, they have not been included in the remaining lease terms.

We lease certain aircraft, facilities, and equipment used in our operations. The related lease agreements, which include both non-cancelable and month-to-month terms, generally provide for fixed monthly rentals, and certain real estate leases also include renewal options. We generally pay all insurance, taxes, and maintenance expenses associated with these leases, and these costs are not included in the lease liability and are recognized in the period in which they are incurred.

Total operating lease expense was $11.4 million and $12.1 million for the three months ended June 30, 2019 and 2018, respectively. For the three months ended June 30, 2019, a portion of the total operating lease expense relating to short-term leases was $1.6 million. The operating lease expense was $22.6 million and $23.8 million for the six months ended June 30, 2019 and 2018, respectively. For the six months ended June 30, 2019, a portion of the total operating lease expense relating to short-term was $3.0 million.

	June 30, 2019
	(Thousands of dollars)
Operating lease right-of-use-assets	$	144,944
Current portion of operating lease liabilities		27,535
Operating lease liabilities		118,167
Total operating lease liabilities	$	145,702
Cash paid for operating leases		21,475
ROU assets obtained in exchange for lease obligations		9,402
Weighted average remaining lease term	5 years
Weighted average discount rate		8.25	%

Maturities of operating lease liabilities at June 30, 2019 are as follows (in thousands):

	Operating
Six Months Ending June 30,	Leases
	Thousands of dollars
Remainder of 2019	$	19,615
2020		37,140
2021		36,297
2022		34,254
2023		23,872
Thereafter		33,975
Total lease payments		185,153
Less imputed interest		(39,451	)
Total	$	145,702

As of December 31, 2018, future total rentals on our non-cancellable operating leases were $160 million in the aggregate, which consisted of the following: $36 million in 2019; $33 million in 2020; $31 million in 2021; $29 million in 2022; $20 million in 2023; and $11 million thereafter.

We are currently in the process of renegotiating certain of our leases in connection with the Chapter 11 Cases. These negotiations, if successfully completed, will likely impact our obligation under our outstanding leases.