Employee benefit plans (Details) - USD ($) $ in Thousands	3 Months Ended	6 Months Ended
Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017	Dec. 31, 2017
Employee benefit plans
Service cost	$ 1,032	$ 680	$ 2,111	$ 1,296
Interest cost	68	52	139	98
Expected return on plan assets	(47)	(38)	(97)	(73)
Amortization of prior service cost	45	13	90	25
Amortization of actuarial losses	66	34	132	68
Net periodic benefit cost	1,164	$ 741	2,375	$ 1,414
Expected contributions	3,200		3,200
Accrued pension obligation	$ 13,700		$ 13,700		$ 13,400

No definition available.

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- Definition

Amount of liability, recognized in statement of financial position, for defined benefit pension plan. Excludes other postretirement benefit plan.

+ References

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-Publisher FASB
-Name Accounting Standards Codification
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- Definition

Amount of gain (loss) from change in actuarial assumptions which (increases) decreases benefit obligation of defined benefit plan. Assumptions include, but are not limited to, interest, mortality, employee turnover, salary, and temporary deviation from substantive plan.

+ References

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- Definition

Amount of prior service cost (credit) recognized in net periodic benefit cost (credit) of defined benefit plan.

+ References

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- Definition

Amount of contributions received and expected to be received by defined benefit plan from employer in current fiscal year.

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- Definition

Amount of expected return (loss) recognized in net periodic benefit (cost) credit, calculated based on expected long-term rate of return and market-related value of plan assets of defined benefit plan.

+ References

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Amount of cost recognized for passage of time related to defined benefit plan.

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Amount of net periodic benefit cost (credit) for defined benefit plan.

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- Definition

Amount of cost for actuarial present value of benefits attributed to service rendered by employee for defined benefit plan.

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