As described in Note 2 – Recent Accounting Pronouncements above, effective January 1, 2019, we adopted Topic 842. We have operating leases for office space and, to a much lesser extent, we also have operating leases for equipment. Our office leases are typically for terms of between 3 and 10 years. Rents usually increase annually in accordance with defined rent steps or based on current year consumer price index adjustments. Some of the lease agreements contain one or more of the following provisions or clauses: tenant allowances, rent holidays, lease premiums, and rent escalation clauses. For the purpose of recognizing these provisions on a straight-line basis over the terms of the leases, we use the date of initial possession to begin amortization, which is generally when we enter the space and begin to make improvements in preparation of intended use or in the case of a lease modification, the date both parties execute the modification. There are typically no purchase options, residual value guarantees or restrictive covenants. When renewal options exist, we generally do not deem them to be reasonably certain to be exercised, and therefore the amounts are not recognized as part of our lease liability nor our right-of-use asset. In certain cases, we sublease excess office space to third party tenants. We do not recognize liabilities or right-of-use assets for leases with an initial term of 12 months or less.

	For the Three Months Ended
	March 31, 2019
Operating lease cost	$	5,890
Variable lease costs		2,914
Short term lease costs		289
Sublease income		(1,780	)
Total net lease cost	$	7,313

	March 31,
	2019
Weighted average remaining lease term (in years):
Operating leases		6

Weighted average discount rate:
Operating leases		5.4	%

The discount rates applied to each lease reflect our estimated incremental borrowing rate. This includes an assessment of our credit rating to determine the rate that we would have to pay to borrow, on a collateralized basis for a similar term, an amount equal to our lease payments in a similar economic environment.

Supplemental cash flow and other information related to leases was as follows (in thousands):

Future minimum lease payments under non-cancellable operating leases were as follows (in thousands):

	March 31,
	2019
2019 (excluding the three months ended March 31, 2019)	$	20,860
2020		25,452
2021		20,328
2022		14,428
2023		12,612
2024 and thereafter		34,798
Total lease payments	$	128,478
Less imputed interest		(20,813	)
Total	$	107,665

As of March 31, 2019, we have additional operating leases that have not yet commenced with obligations of $2.4 million. These operating leases expected to commence in 2019 with lease terms of 1 year to 5 years.

Future minimum annual lease payments for the years subsequent to December 31, 2018 and in the aggregate were as follows (shown in thousands):

Year ending December 31,	Amount
2019	$	27,496
2020		25,583
2021		20,742
2022		14,747
2023		12,873
Thereafter		35,077
	$	136,518

Rent expense for operating leases was $25.3 million for the year ended December 31, 2018.

For the Three Months Ended March 31,

Cash paid for amounts included in the measurement of lease liabilities:

Operating cash flows from operating leases