Note 5 - Stock-based Compensation

6 Months Ended

Jun. 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

$4.9

million and

$3.7

million for the

three

months ended

June 30, 2017

and

2016,

respectively. For the

six

months ended

June 30, 2017

and

2016,

we recognized stock-based compensation expense of

$9.2

million and

$7.5

million, respectively. As of

June 30, 2017,

total unrecognized stock-based compensation expense was

$36.6

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

2.1years.