What is the average Net deferred tax liabilities for December 31, 2018 to 2019?
{"Deferred tax liabilities:   -- Vessels and other property (1)": {"2019": 128026, "2018": 128226}, "Deferred tax liabilities:   -- Prepaid expenditures": {"2019": 5621, "2018": 7108}, "Deferred tax liabilities:   -- Operating lease right-of-use assets": {"2019": 72298, "2018": "\u2014"}, "Deferred tax liabilities:   -- Other-net": {"2019": 2, "2018": 4}, "Deferred tax liabilities:   -- Total deferred tax liabilities": {"2019": 205947, "2018": 135338}, "Deferred tax assets: -- Loss carryforwards": {"2019": 68917, "2018": 66737}, "Deferred tax assets: -- Operating lease liability": {"2019": 71779, "2018": "\u2014"}, "Deferred tax assets: -- Finance lease liability": {"2019": 6333, "2018": "\u2014"}, "Deferred tax assets: -- Employee compensation and benefit plans": {"2019": 3869, "2018": 4287}, "Deferred tax assets: -- Financing and professional fees": {"2019": 2003, "2018": 1859}, "Deferred tax assets: -- Accrued expenses and other": {"2019": 1165, "2018": 51}, "Deferred tax assets: -- Total deferred tax assets": {"2019": 154066, "2018": 72934}, "Deferred tax assets: -- Valuation allowance": {"2019": 20952, "2018": 10961}, "Deferred tax assets: -- Net deferred tax assets": {"2019": 133114, "2018": 61973}, "Deferred tax assets: -- Net deferred tax liabilities": {"2019": 72833, "2018": 73365}}
net_deferred_tax_liabilities_2019 = df["Deferred tax assets: -- Net deferred tax liabilities"]["2019"]
net_deferred_tax_liabilities_2018 = df["Deferred tax assets: -- Net deferred tax liabilities"]["2018"]
other_net_2019 = df["Deferred tax liabilities:   -- Other-net"]["2019"]
answer = (net_deferred_tax_liabilities_2019 + net_deferred_tax_liabilities_2018) / other_net_2019