Note 5 - Stock-based Compensation

9 Months Ended

Sep. 30, 2017

Notes to Financial Statements

Disclosure of Compensation Related Costs, Share-based Payments [Text Block]

5

.      

Stock-Based Compensation

We account for share-based awards in accordance with

ASC Topic 

718,

Compensation – Stock Compensation

("ASC

718"

), which requires that the cost resulting from all share-based payment transactions be recognized in the financial statements. ASC

718

requires all entities to apply a fair value-based measurement method in accounting for share-based payment transactions with employees except for equity instruments held by employee share ownership plans.

Total compensation expense recognized related to stock-based compensation was

$5.1

million and

$3.7

million for the

three

months ended

September 30, 2017

and

2016,

respectively. For the

nine

months ended

September 30, 2017

and

2016,

we recognized stock-based compensation expense of

$14.3

million and

$11.2

million, respectively. As of

September 30, 2017,

total unrecognized stock-based compensation expense was

$31.3

million, with a weighted average period over which the remaining unrecognized compensation expense is expected to be recorded of approximately

2.2

years.