11. Income Taxes:

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


	December 31,
	2015		2014		2013
Federal:
Current	$	168,596	$	167,745	$	134,938
Deferred		12,866		2,262		14,784

		181,462		170,007		149,722

State:
Current		20,948		21,109		17,037
Deferred		1,628		297		1,136

		22,576		21,406		18,173

Total	$	204,038	$	191,413	$	167,895

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

The effective tax rate was 37.76%, 37.63% and 37.44% for the years ended December 31, 2015, 2014 and 2013, respectively.

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


	December 31,
	2015			2014			2013
Tax at statutory rate		35.00	%		35.00	%		35.00	%
State income tax, net of federal benefit		2.97			2.74			2.63
Non-deductible expenses		0.34			0.33			0.27
Change in accrual estimates relating to uncertain tax positions		(0.43	)		(0.59	)		(0.48	)
Change in valuation allowance		0.29			—			—
Other, net		(0.41	)		0.15			0.02

Income tax provision		37.76	%		37.63	%		37.44	%

The Company adopted the accounting guidance related to deferred income taxes, and accordingly, all deferred tax assets and liabilities are classified as long-term for the year ended December 31, 2015. The significant components of deferred income tax assets and liabilities are as follows (in thousands):


	December 31, 2015
Allowance for uncollectible accounts	$	82,928
Reserves and accruals		66,655
Stock-based compensation		13,662
Net operating loss carryforward		51,505
Property and equipment		3,116
Other		2,723

Deferred tax assets before valuation allowance		220,589
Less: Valuation allowance		(1,552	)

Deferred tax assets, net of valuation allowance		219,037

Gross deferred tax liabilities:
Amortization		(311,303	)
Accrual to cash adjustment		(55,046	)
Other		(6,693	)

Total deferred tax liabilities		(373,042	)

Net deferred tax liability	$	(154,005	)

Deferred income tax assets and liabilities have not been retrospectively classified as long-term for the year ended December 31, 2014. The significant components of deferred tax assets and liabilities for the year ended December 31, 2014 are as follows (in thousands):


	December 31, 2014
	Total			Current			Non- Current
Allowance for uncollectible accounts	$	48,178		$	48,178		$	—
Reserves and accruals		62,708			26,066			36,642
Stock-based compensation		14,354			8,346			6,008
Net operating loss carryforward		10,933			1,504			9,429
Property and equipment		1,524			—			1,524
Other		1,461			583			878

Total deferred tax assets		139,158			84,677			54,481

Amortization		(214,968	)		—			(214,968	)
Accrual to cash adjustment		(38,524	)		(38,524	)		—
Other		(192	)		(192	)		—

Total deferred tax liabilities		(253,684	)		(38,716	)		(214,968	)

Net deferred tax (liability) asset	$	(114,526	)	$	45,961		$	(160,487	)

The income tax benefit related to 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 in excess of amounts recorded as equity compensation expense reduces taxes currently payable and is credited to additional paid-in capital. Such amounts totaled approximately $11.6 million, $17.5 million, and $19.0 million for the years ended December 31, 2015, 2014 and 2013, respectively.

The Company has net operating loss carryforwards for federal and state tax purposes totaling approximately $136.6 million, $29.0 million, and $16.9 million at December 31, 2015, 2014 and 2013, respectively, expiring at various times in 2019 through 2035. The changes in net operating loss carryforwards in 2015 and 2014 are primarily due to timing differences related to the recognition of income for tax purposes associated with acquisitions.

As of December 31, 2015, 2014 and 2013, the Company’s liability for uncertain tax positions, excluding accrued interest and penalties, was $18.4 million, $17.2 million and $14.9 million, respectively. The Company had approximately $17.1 million of uncertain tax positions that, if recognized, would favorably impact its effective tax rate at December 31, 2015.

The following table summarizes the activity related to the Company’s liability for uncertain tax positions for the years ended December 31, 2015, 2014 and 2013 (in thousands):


	Years Ended December 31,
	2015			2014			2013
Balance at beginning of year	$	17,165		$	14,902		$	13,072
Increases related to prior year tax positions		467			40			338
Decreases related to prior year tax positions		(1,168	)		—			(38	)
Increases related to current year tax positions		3,675			3,750			2,955
Decreases related to lapse of statutes of limitations		(1,692	)		(1,527	)		(1,425	)

Balance at end of year	$	18,447		$	17,165		$	14,902

During the years ended December 31, 2015 and 2014, the Company increased its liability for uncertain tax positions by a total of $1.2 million and $2.3 million, respectively, primarily related to additional taxes on current year positions, partially offset by decreases due to the expiration of statutes of limitation and current year tax positions.

During the third quarter of 2015, the Company entered into settlement discussions with a taxing authority regarding a tax matter. In connection with these settlement discussions, the Company believes that it is reasonably possible that its liability for uncertain tax positions may be decreased by approximately $7.0 million to $9.0 million over the next 12 months, all of which would favorably impact the Company’s effective tax rate.

In addition, the Company anticipates that its liability for uncertain tax positions will be increased by approximately $2.5 million for additional taxes and decreased by approximately $1.9 million related to the expiration of certain statutes of limitation over the next 12 months.

The Company includes interest and penalties related to income tax liabilities in income tax expense. The Company recognized a net increase of $0.6 million and $0.3 million related to interest and penalties during the years ended December 31, 2015 and 2014, respectively. The Company recognized a net decrease of $0.6 million in interest and penalties related to income tax liabilities during the year ended December 31, 2013. At December 31, 2015 and 2014, the Company’s accrued liability for interest and penalties related to income tax liabilities totaled $9.3 million and $8.7 million, respectively.

The Company is currently subject to U.S. Federal and various state income tax examinations for the tax years 2004 through 2014.