Stock-Based Compensation and 401(k) Retirement Savings Plan

The Company believes that stock-based compensation aligns the interests of its employees and directors with those of its stockholders. Stock-based compensation provides incentives to retain and motivate executive officers and key employees responsible for driving Company performance and maintaining important relationships that contribute to the growth of the Company. In 2015, the Company issued shares for restricted stock units ("RSUs"), stock options, and a stock award.

Stock-based compensation expense is included in SG&A expenses in the accompanying consolidated statements of operations and comprehensive income and was classified as follows (in thousands):



	Year Ended December 31,
	2015		2014		2013
Continuing operations	$	22,018	$	15,623	$	13,533
Discontinued operations	—		576		878
Total	$	22,018	$	16,199	$	14,411

The Company recognized an income tax benefit for stock-based compensation arrangements of $6.6 million, $4.7 million and $5.1 million in 2015, 2014 and 2013, respectively. As of December 31, 2015, there were 2,546,962 shares available for issuance under the Company's stock- based compensation plans.

Restricted Stock Units

The fair value of each RSU is based on the fair market value of the awards on the grant date and the Company records compensation expense based on this value, net of a forfeiture rate. The forfeiture rate estimates the number of awards that will eventually vest and is based on historical vesting patterns for RSUs.

A summary of the status of the Company’s unvested RSUs as of December 31, 2015 and changes during the year then ended are presented below:



	Service Conditions		Performance and Service Conditions		Total		Weighted Average Grant-Date Fair Value Per Unit
Unvested RSUs outstanding at December 31, 2014	705,373		381,188		1,086,561			$	24.88
Granted	213,649		712,108		925,757			$	40.49
Market value share count adjustment for liability awards	—		18,619		18,619			$	35.09
Vested	(423,280	)	(204,936	)	(628,216	)		$	24.76
Forfeited	(30,373	)	(25,728	)	(56,101	)		$	31.38
Unvested RSUs outstanding at December 31, 2015	465,369		881,251		1,346,620			$	36.31
Unvested and expected to vest RSUs outstanding at December 31, 2015	437,699		826,620		1,264,319			$	36.05

The total number of shares vested in the table above includes 229,366 shares surrendered by the employees to the Company for payment of income taxes. The surrendered shares are available for issuance under the Plan.

The weighted-average grant-date fair value of RSUs granted during 2015, 2014 and 2013 was $40.49, $33.66 and $26.17 per award, respectively. The total intrinsic value of RSUs that vested during 2015, 2014 and 2013, was $24.3 million, $21.3 million and $15.0 million, respectively.

As of December 31, 2015, there was unrecognized compensation expense of $30.9 million related to unvested RSUs based on awards that are expected to vest. The unrecognized compensation expense is expected to be recognized over a weighted-average period of two years.

Liability Awards

Liability awards have a performance component and vest over one to three years. The performance goals are approved by the Compensation Committee of the Company’s Board of Directors. The Company classifies these awards as liabilities until the number of shares is determined, in accordance with the grant. The number of shares is determined by dividing the final award liability balance by the Company’s closing stock price on the settlement dates. This liability is included in other accrued expenses in the accompanying Consolidated Balance Sheets.

The following table summarizes the balance of liability awards and changes during the years presented (in thousands):



	2015			2014			2013
Balances of liability awards at beginning of year	$	1,453		$	2,500		$	2,000
Granted	—			500			1,000
Settled	(1,453		)	(1,497		)	(500		)
Canceled	—			(50		)	—
Balance of liability awards end of year	$	—		$	1,453		$	2,500

There was no expense related to liability awards during 2015 and the expense in 2014 and 2013 was $0.5 million and $1.0 million, respectively. There was no unrecognized compensation expense for liability awards as of December 31, 2015.

Stock Options

Subsequent to 2012 the Company has not granted any stock options. The fair value of stock option grants was estimated on the grant date using the Black-Scholes option pricing model. The Company records compensation expense based on this value, net of a forfeiture rate. The forfeiture rate estimates the number of awards that will eventually vest and is based on historical vesting patterns for stock options. The following summarizes pricing and term information for options outstanding as of December 31, 2015:



					Options Outstanding					Options Exercisable
					Number Outstanding at	Weighted Average Remaining Contractual Life (years)	Weighted Average Exercise Price			Number Exercisable at	Weighted Average Exercise Price
Range of Exercise Prices					December 31, 2015	Weighted Average Remaining Contractual Life (years)	Weighted Average Exercise Price			December 31, 2015	Weighted Average Exercise Price
$	4.44	-	$	8.26	73,901	4.0		$	6.96	73,305		$	6.95
$	10.46	-	$	11.75	61,885	4.3		$	10.88	60,755		$	10.89
$	12.90	-	$	12.90	120,000	1.1		$	12.90	120,000		$	12.90
$	13.31	-	$	13.58	25,600	1.4		$	13.33	25,506		$	13.32
$	16.51	-	$	16.51	75,000	6.7		$	16.51	60,937		$	16.51
$	4.44	-	$	16.51	356,386	3.5		$	12.11	340,503		$	11.94

The following table is a summary of stock option activity during 2015:



	Incentive Stock Options		Non- Qualified Stock Options		Total		Weighted Average Exercise Price Per Share		Weighted Average Remaining Contractual Term (Years)		Aggregate Intrinsic Value
Outstanding at December 31, 2014	4,267		690,614		694,881		$	11.33		3.5	$	15,189,000
Exercised	(4,267	)	(325,235	)	(329,502	)	$	10.54
Canceled	—		(8,993	)	(8,993	)	$	9.81
Outstanding at December 31, 2015	—		356,386		356,386		$	12.11		3.5	$	11,705,000
Vested and Expected to Vest at December 31, 2015	—		356,386		356,386		$	12.11		3.5	$	11,705,000
Exercisable at December 31, 2015	—		340,503		340,503		$	11.94		3.3	$	11,241,000

The total intrinsic value of options exercised during 2015, 2014 and 2013 was $10.9 million, $3.9 million, and $7.6 million, respectively.

Employee Stock Purchase Plan

The On Assignment 2010 Employee Stock Purchase Plan, as amended ("ESPP") allows eligible employees to purchase common stock of the Company at a 15 percent discount to the market price as stipulated by the plan. Under the ESPP, 3,500,000 shares of common stock were reserved for issuance when it was approved on June 3, 2010 by the Company's stockholders. Shares of common stock are transferred to participating employees at the conclusion of each six-month offering period, which ends on the last business day of the month in March and September each year. Compensation expense is measured using a Black-Scholes option-pricing model. The table below presents the average fair value per share of shares purchased, and the compensation expense under the ESPP (dollars in thousands, except per share amounts):



Year Ended December 31,	Average fair value per share	Shares	Expense
2015	$7.77	204,401	$	1,586
2014	$8.35	207,805	$	1,756
2013	$7.16	203,200	$	1,195

401(k) Retirement Savings Plan

The Company maintains various 401(k) retirement savings plans for the benefit of eligible employees. Under terms of these plans, eligible employees are able to make contributions to these plans on a tax-deferred basis. The Company makes matching contributions, some of which are discretionary. The Company made contributions to the 401(k) plans of $7.6 million, $7.5 million and $6.0 million for the years ended December 31, 2015, 2014 and 2013, respectively.