Income taxes (Tables)

12 Months Ended

Dec. 31, 2019

Income Tax Disclosure [Abstract]

Summary of difference between statutory federal income tax rate on income before income taxes and effective income tax rate

The difference between the statutory federal income tax rate on income before income taxes and our effective income tax rate is summarized as follows:

	2019		2018		2017
Statutory federal income tax rate	21.0	%	21.0	%	35.0	%
Patronage exclusion	(21.0)	%	(20.8)	%	(34.1)	%
AMT credit monetization	0.0	%	0.0	%	2.2	%
Other	0.0	%	(0.2)	%	(0.9)	%
Effective income tax rate	0.0	%	0.0	%	2.2	%

Schedule of components of net deferred tax assets and liabilities

The components of our net deferred tax assets and liabilities as of December 31, 2019 and 2018 were as follows:

	(dollars in thousands)
	2019		2018
Deferred tax assets
Net operating losses	$	1,123	$	3,830
Tax credits (alternative minimum tax and other)	—		—
Accounting for Rocky Mountain transactions	231,844		231,543
Advance payments	74,482		46,708
Other assets	88,821		82,655
Deferred tax assets	396,270		364,736
Less: Valuation allowance	(1,123)		(3,830)
Net deferred tax assets	$	395,147	$	360,906
Deferred tax liabilities
Depreciation	$	258,724	$	268,039
Accounting for Rocky Mountain transactions	118,021		116,226
Other liabilities	68,035		75,691
Deferred tax liabilities	444,780		459,956
Net deferred tax liabilities	49,633		99,050
Less: Patronage exclusion	(49,633)		(99,050)
Net deferred taxes	$	—	$	—