Stockholders' equity (Tables)

3 Months Ended

Mar. 31, 2019

Stockholders' equity

Summary of stock option activity

The following table summarizes stock option activity for the three months ended March 31, 2019 (shares and intrinsic value in thousands):

				Weighted-average
		Weighted-average		remaining contractual	Aggregate intrinsic
	Number of shares	exercise price		term	value
Outstanding at December 31, 2018	2,910	$	11.62	5.6	$	2,806
Granted	—		—	—		—
Exercised	—		—	—		—
Forfeited	—		—	—		—
Expired	—		—	—		—
Outstanding at March 31, 2019	2,910	$	11.62	5.4	$	7,547
Vested at March 31, 2019	2,195	$	11.71	5.0	$	5,559
Exercisable at March 31, 2019	2,195	$	11.71	5.0	$	5,559

Summary of restricted share activity

The following table summarizes restricted share activity for the three months ended March 31, 2019 (shares in thousands):

		Weighted-average
	Number of shares	grant date fair value
Outstanding at December 31, 2018	370	$	9.86
Granted	—		—
Vested	—		—
Forfeited	—		—
Outstanding at March 31, 2019	370	$	9.86

Time Based Stock Option | Black Scholes Pricing Model

Stockholders' equity

Schedule of valuation assumptions

	Three Months Ended	Year Ended
Black-Scholes Option Valuation Assumptions	March 31, 2019	December 31, 2018
Risk-free interest rate	—	2.7% - 3.0	%
Dividend yield	—	—
Volatility	—	39.0% - 41.0	%
Weighted-average expected term (years)	—	6.0