11. Income Taxes:

The components of the income tax provision (benefit) are as follows (in thousands):


	December 31,
	2018			2017			2016
Federal:
Current	$	97,754		$	130,053		$	166,758
Deferred		(20,176	)		(63,038	)		15,596

		77,578			67,015			182,354

State:
Current		26,605			20,070			4,296
Deferred		(3,973	)		2,965			2,553

		22,632			23,035			6,849

Total	$	100,210		$	90,050		$	189,203

The Company files its tax return on a consolidated basis with its subsidiaries, and its affiliated professional contractors file tax returns on an individual basis.

Beginning on January 1, 2018, the Company’s statutory tax rate was reduced from 35.0% to 21.0% as a result of legislation enacted under the Tax Cuts and Jobs Act of 2017 (“TCJA”). The effective tax rate was 27.2%, 21.9% and 36.8% for the years ended December 31, 2018, 2017 and 2016, respectively. During the three months ended December 31, 2017, the Company recorded a $70.0 million income tax benefit related to the reduction of its net deferred tax liability resulting from the reduction in the corporate tax rate under the TCJA. During the three months ended September 30, 2016, the Company settled a certain tax matter with a taxing authority. In connection with this settlement, the Company’s effective income tax rate was favorably impacted by $10.6 million.

The differences between the effective rate and the United States federal income tax statutory rate are as follows:


	December 31,
	2018			2017			2016
Tax at statutory rate		21.00	%		35.00	%		35.00	%
State income tax, net of federal benefit		4.80			3.33			2.94
Non-deductible expenses		0.44			0.49			0.43
Change in accrual estimates relating to uncertain tax positions		0.05			0.02			(2.11	)
Change in valuation allowance		—			—			0.48
Other, net		1.20			0.16			0.06
Change in tax law		(0.32	)		(17.06	)		—

Income tax provision		27.17	%		21.94	%		36.80	%

All of the Company’s deferred tax assets and liabilities are classified as long-term. The significant components of deferred income tax assets and liabilities are as follows (in thousands):


	December 31,
	2018			2017
Allowance for uncollectible accounts	$	194,876		$	80,056
Reserves and accruals		59,270			45,454
Stock-based compensation		9,201			7,975
Net operating loss carryforward		25,226			28,569
Property and equipment		26			685
Other		1,197			970

Deferred tax assets before valuation allowance		289,796			163,709
Less: Valuation allowance		(2,628	)		(2,615	)

Deferred tax assets, net of valuation allowance		287,168			161,094

Gross deferred tax liabilities:
Amortization		(286,552	)		(258,618	)

Accounting method changes		(109,418	)		(4,150	)
Accrual to cash adjustment		(39	)		(31,290	)
Other		(489	)		—

Total deferred tax liabilities		(396,498	)		(294,058	)

Net deferred tax liability	$	(109,330	)	$	(132,964	)

The Company’s net deferred tax liability decreased by $23.6 million during 2018. During 2018, certain of the Company’s affiliated professional contractors elected to change their method of accounting from cash basis to accrual basis for income tax purposes. During the year ended December 31, 2018, the increases in allowance for uncollectible accounts of $114.8 million and accounting method changes of $105.3 million as well as the decrease in accrual to cash adjustment of $31.3 million primarily relate to these accounting method changes.

Beginning January 1, 2017, excess tax benefits or deficiencies associated with the exercise of stock options, the vesting of restricted and deferred stock and the purchase of shares under the Company’s non-qualified employee stock purchase plan are recognized as income tax benefits or expenses in the income statement in the reporting period in which they occur instead of an increase or decrease to additional paid-in-capital. For the years ended December 31, 2018 and 2017, income tax expense of $1.4 million and $0.2 million, respectively, was recognized for excess tax deficiencies. For the year ended December 31, 2016, additional paid-in-capital was increased by $4.2 million for excess tax benefits.

The Company has net operating loss carryforwards for federal and state tax purposes totaling $101.9 million, $116.0 million and $130.0 million at December 31, 2018, 2017 and 2016, respectively. With respect to the December 31, 2018 balance, approximately $74.3 million expires at various times from 2019 through 2038, and $27.6 million does not expire.

As of December 31, 2018, 2017 and 2016, the Company’s liability for uncertain tax positions, excluding accrued interest and penalties, was $11.2 million, $11.0 million and $9.5 million, respectively. As of December 31, 2018, the Company had $10.9 million of uncertain tax positions that, if recognized, would favorably impact its effective tax rate.

The following table summarizes the activity related to the Company’s liability for uncertain tax positions for the years ended December 31, 2018, 2017 and 2016 (in thousands):


	Years Ended December 31,
	2018			2017			2016
Balance at beginning of year	$	10,972		$	9,469		$	18,447
Increases related to prior year tax positions		385			2,284			301
Decreases related to prior year tax positions		—			(143	)		(3,927	)
Increases related to current year tax positions		2,900			1,430			2,258
Settlements		—			—			(5,644	)
Decreases related to lapse of statutes of limitation		(3,072	)		(2,068	)		(1,966	)

Balance at end of year	$	11,185		$	10,972		$	9,469

During the years ended December 31, 2018 and 2017, the Company increased its liability for uncertain tax positions by a total of $0.2 million and $1.5 million, respectively, primarily related to additional taxes on current and prior year positions, partially offset by the expiration of statutes of limitation. In addition, the Company anticipates that its liability for uncertain tax positions will increase by $0.2 million over the next 12 months.

The Company includes interest and penalties related to income tax liabilities in income tax expense. The income tax benefit recognized by the Company for interest and penalties during the year ended December 31, 2018 was nominal. The Company recognized income tax benefits of $0.2 million and $7.9 million related to interest and penalties during the years ended December 31, 2017 and 2016, respectively. At December 31, 2018 and 2017, the Company’s accrued liability for interest and penalties related to income tax liabilities totaled $1.1 million and $1.2 million, respectively.

The Company is currently subject to U.S. Federal and various state income tax examinations for the tax years 2014 through 2017.