Stock-based Compensation
Stock-based compensation expense for the years ended December 31, 2017, 2016, and 2015 was $26.5 million, or 3% of revenue, $31.8 million, or 3% of revenue, and $34.1 million, or 4% of revenue, respectively.
We account for stock-based payment awards in accordance with ASC 718, Stock Compensation, which requires stock-based compensation expense to be recognized based on the fair value of such awards on the date of grant. We amortize compensation cost on a graded vesting basis over the vesting period, after assessing the probability of achieving requisite performance criteria with respect to performance-based awards. Stock-based compensation cost is recognized over the requisite service period for each separately vesting tranche of the award as though the award were, in substance, multiple awards. This has the impact of greater stock-based compensation expense recognized during the initial years of the vesting period for awards with multiple tranches.
Stock-based compensation expenses decreased by $5.3 million, or 17% in 2017 compared with 2016 primarily due to reduced probability of achieving certain performance based awards and delayed annual award grants, partially offset by increased ESPP expense resulting from higher employee participation compared to the prior year.
Stock-based compensation expense decreased by $2.2 million, or 7% in 2016 compared with 2015 because forfeitures were greater than the previous forfeiture estimate that was used prior to implementation of ASU2016-09, prior year forfeitures resulting from the resignation of our chief financial officer in January 2015, reduced probability of achieving performance awards, and decreased ESPP participation by employees compared to the prior year.
Amortization of Identified Intangibles
Amortization of identified intangibles for the years ended December 31, 2017, 2016, and 2015 was $47.3 million, or 5% of revenue, $39.6 million, or 4% of revenue, and $26.5 million, or 3% of revenue, respectively.
Amortization of identified intangibles increased by $7.7 million, or 20% in 2017 compared with 2016 primarily due to amortization of identified intangibles resulting from the Escada, Generation Digital, CRC, and FFPS acquisitions as well as full year amortization expense recognized on 2016 acquisitions, partially offset by decreased amortization due to certain intangible assets from prior year acquisitions becoming fully amortized.
Amortization of identified intangibles increased by $13.0 million, or 49% in 2016 compared with 2015 primarily due to intangible amortization of identified intangibles resulting from the Reggiani, Matan, CTI, Shuttleworth, Rialco, and Optitex acquisitions, partially offset by decreased amortization due to certain intangible assets from prior year acquisitions becoming fully amortized.
Restructuring and Other
Restructuring and other costs for the years ended December 31, 2017, 2016, and 2015 were $7.6, $6.7, and $5.7 million, respectively. Restructuring and other charges include severance costs of $4.7, $4.1, and $3.0 million related to head count reductions of 144, 128, and 99 for the years ended December 31, 2017, 2016, and 2015, respectively. Severance costs include severance payments, related employee benefits, retention bonuses, outplacement fees, recruiting, and relocation costs.
Facilities relocation and downsizing expenses for the years ended December 31, 2017, 2016, and 2015 were $0.6, $0.5, and $0.9 million, respectively. Facilities restructuring and other expenses are primarily related to the relocation of certain manufacturing and administrative locations to accommodate decreased space requirements in 2017 and additional space requirements in 2016 and 2015. Integration expenses for the years ended December 31, 2017, 2016, and 2015 of $2.3, $2.1, and $1.8 million, respectively, were required to integrate our business acquisitions.
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