Federal and State Income Taxes (Tables)

12 Months Ended

Dec. 31, 2017

Income Tax Disclosure [Abstract]

Summary of consolidated income tax expense

The following table is a summary of consolidated income tax expense:

	Years ended
(Dollars in thousands)	December 31, 2017		December 31, 2016		December 31, 2015
Current
Federal	$	29,555	30,461		28,705
State	9,183		9,283		9,374
Total current income tax expense	38,738		39,744		38,079
Deferred 1
Federal	22,246		(70	)	(3,451	)
State	3,641		(12	)	(629	)
Total deferred income tax expense (benefit)	25,887		(82	)	(4,080	)
Total income tax expense	$	64,625	39,662		33,999

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¹  Includes tax benefit of operating loss carryforwards of $644,000, $571,000 and $391,000 for the years ended December 31, 2017, 2016, and 2015, respectively.

Summary of effective tax rate

Combined federal and state income tax expense differs from that computed at the federal statutory corporate tax rate as follows:

	Years ended
	December 31, 2017		December 31, 2016		December 31, 2015
Federal statutory rate	35.0	%	35.0	%	35.0	%
State taxes, net of federal income tax benefit	4.6	%	3.8	%	3.7	%
Tax rate change	10.9	%	—	%	—	%
Tax-exempt interest income	(10.5	)%	(12.2	)%	(12.6	)%
Tax credits	(3.2	)%	(2.1	)%	(3.0	)%
Other, net	(1.1	)%	0.2	%	(0.5	)%
Effective tax rate	35.7	%	24.7	%	22.6	%

Summary of net deferred tax asset

The tax effect of temporary differences which give rise to a significant portion of deferred tax assets and deferred tax liabilities are as follows:

(Dollars in thousands)	December 31, 2017			December 31, 2016
Deferred tax assets
Allowance for loan and lease losses	$	32,890		50,172
Deferred compensation	5,640			8,320
Other real estate owned	5,126			8,309
Acquisition fair market value adjustments	4,139			4,763
Net operating loss carryforwards	2,841			4,737
Employee benefits	2,615			3,927
Interest rate swap agreements	2,379			5,705
Other	3,673			5,569
Total gross deferred tax assets	59,303			91,502
Deferred tax liabilities
Deferred loan costs	(5,854		)	(8,061	)
Intangibles	(4,161		)	(5,477	)
Depreciation of premises and equipment	(2,863		)	(3,111	)
FHLB stock dividends	(2,602		)	(3,976	)
Available-for-sale securities	(1,707		)	(1,036	)
Debt modification costs	(1,591		)	—
Other	(2,181		)	(2,720	)
Total gross deferred tax liabilities	(20,959		)	(24,381	)
Net deferred tax asset	$	38,344		67,121

Income tax return jurisdictions and years subject to examination

The following schedule summarizes the years that remain subject to examination as of December 31, 2017:

	Years ended December 31,
Federal	2013, 2014, 2015 and 2016
Montana	2014, 2015 and 2016
Idaho	2014, 2015 and 2016
Utah	2014, 2015 and 2016
Colorado	2013, 2014, 2015 and 2016
Arizona	2013, 2014, 2015 and 2016