Stockholders' equity (Tables)

12 Months Ended

Dec. 31, 2018

Equity [Abstract]

Disclosure of Share-based Compensation Arrangements by Share-based Payment Award [Table Text Block]

The Company had the following shares of common stock reserved for issuance upon the exercise of equity instruments as of December 31, 2018:

(in thousands)	December 31, 2018
Stock options outstanding	5,993
Restricted stock units outstanding	7,217
Performance stock units outstanding	300
Common stock available for future grants	31,421
Total common stock shares reserved for issuance	44,931