The following table presents the total stock-based compensation expense resulting from stock option awards, RSUs, PSUs, and the ESPP included in SG&A in the Condensed Consolidated Statements of (Loss) Income:

In millions
	Three Months Ended September 30,				Nine Months Ended September 30,
	2019		2018		2019		2018
Stock option plan	$	0.9	$	2.5	$	6.8	$	8.4
RSUs		2.0		2.0		6.0		5.8
PSUs		0.5		1.9		0.2		4.5
ESPP		0.3		0.3		0.7		0.8
Total expense	$	3.7	$	6.7	$	13.7	$	19.5

The decrease in expense during the three and nine months ended September 30, 2019, as compared to the three and nine months ended September 30, 2018, was primarily the result of a lower estimated PSU achievement of 2019 performance goals and higher award forfeitures.

Stock option activity for the nine months ended September 30, 2019 is summarized as follows:

	Number of Options			Weighted Average Exercise Price per Share		Weighted Average Remaining Contractual Life		Total Aggregate Intrinsic Value
						(in years)		(in millions)
Outstanding at January 1, 2019		4,896,386		$	95.85
Granted		340,652			49.01
Exercised		(267,566	)		51.50
Forfeited		(387,082	)		89.17
Canceled or expired		(373,137	)		97.89
Outstanding as of September 30, 2019		4,209,253		$	95.37		3.2	$	0.8
Exercisable as of September 30, 2019		3,351,023		$	100.83		2.5	$	-

At September 30, 2019, the Company had $11.2 million of total unrecognized compensation expense related to stock options, which is expected to be recognized over a weighted average period of 2.5 years. Current period grants vest over a period of three years.

There were no options exercised in the three months ended September 30, 2019. For the three months ended September 30, 2018, the intrinsic value of options exercised was $3.3 million. For the nine months ended September 30, 2019 and 2018, the intrinsic value of options exercised was $1.5 million and $4.8 million, respectively. The exercise intrinsic value represents the total pre-tax intrinsic value (the difference between the fair value on the trading day the option was exercised and the exercise price associated with the respective option).

The estimated fair value of stock options at the time of the grant using the Black-Scholes option pricing model was as follows:

	Three Months Ended September 30,						Nine Months Ended September 30,
	2019			2018			2019			2018
Stock options granted (shares)		30,666			1,712			340,652			362,382
Weighted average fair value at grant date	$	13.74		$	18.09		$	14.41		$	16.87
Assumptions:
Expected term (in years)		4.34			4.89			4.40			4.89
Expected volatility		32.63	%		25.68	%		30.99	%		25.34	%
Expected dividend yield		0.00	%		0.00	%		0.00	%		0.00	%
Risk free interest rate		1.76	%		2.74	%		2.35	%		2.58	%

RSU activity for the nine months ended September 30, 2019 is summarized as follows:

	Number of Units			Weighted Average Grant Date Fair Value		Weighted Average Remaining Contractual Life		Total Aggregate Intrinsic Value
						(in years)		(in millions)
Non-vested at January 1, 2019		429,810		$	72.02
Granted		262,864			48.57
Vested and released		(105,677	)		73.47
Forfeited		(115,001	)		69.30
Non-vested as of September 30, 2019		471,996		$	59.12		1.6	$	24.0

At September 30, 2019, the Company had approximately $21.8 million of total unrecognized compensation expense related to RSUs, which is expected to be recognized over a weighted average period of 2.7 years. The fair value of RSUs that vested during the three and nine months ended September 30, 2019 was $0.3 million and $5.1 million, respectively. Current period grants vest over a period of three years.

PSU activity for the nine months ended September 30, 2019, is summarized as follows:

	Number of Units			Weighted Average Grant Date Fair Value
Non-vested at January 1, 2019		115,508		$	63.77
Granted		157,451			48.59
Vested and released		(65,095	)		63.38
Forfeited		(84,936	)		58.11
Non-vested as of September 30, 2019		122,928		$	48.45

At September 30, 2019, the Company had approximately $0.6 million of total unrecognized compensation expense related to the 2019 installments of PSUs. At September 30, 2019, approximately 227,000 of additional installments of PSUs exist which will vest, or not, based on achievement of performance goals to be established for fiscal years 2020 through 2021.