v3.19.1

Stock incentive plans - Stock option awards (Details) - Stock options - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended	12 Months Ended
	Mar. 31, 2019	Dec. 31, 2018
Stock incentive plans
Vesting period	4 years
Number of Options
Outstanding at beginning of period (in shares)	304
Exercised (in shares)	(4)
Canceled/forfeited (in shares)	0
Outstanding and exercisable at end of period (in shares)	300	304
Weighted Average Exercise Price
Outstanding at beginning of period (in dollars per share)	$ 7.49
Exercised (in dollars per share)	2.01
Outstanding and exercisable at end of period (in dollars per share)	$ 7.55	$ 7.49
Weighted-Average Remaining Contract Life (years)
Outstanding and exercisable at end of period	3 years 7 months 6 days	3 years 9 months 18 days
Aggregate Intrinsic Value
Outstanding and exercisable at end of period	$ 4,766	$ 3,970
Vesting in 12 months
Stock incentive plans
Vesting period	12 months
Vesting percentage	25.00%
Vesting monthly 12 months after grant date
Stock incentive plans
Vesting percentage	75.00%

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The number of shares under options that were cancelled during the reporting period as a result of occurrence of a terminating event specified in contractual agreements pertaining to the stock option plan.

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Amount by which the current fair value of the underlying stock exceeds the exercise price of options outstanding.

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Number of options outstanding, including both vested and non-vested options.

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Weighted average price at which grantees can acquire the shares reserved for issuance under the stock option plan.

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