Condensed Consolidated Statements of Comprehensive Income - USD ($) $ in Thousands	3 Months Ended	6 Months Ended
Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Statement of Comprehensive Income [Abstract]
Net income	$ 7,527	$ 6,369	$ 16,454	$ 15,047
Other comprehensive income (loss), net of tax:
Change in post-employment benefits	41	(38)	28	(77)
Other, net of tax	0	(2)	0	(4)
Other comprehensive income (loss)	41	(40)	28	(81)
Comprehensive income	$ 7,568	$ 6,329	$ 16,482	$ 14,966

Other Comprehensive Income (Loss), Other Reclassification Adjustment from AOCI, Net of Tax

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Amount after tax of increase (decrease) in equity from transactions and other events and circumstances from net income and other comprehensive income, attributable to parent entity. Excludes changes in equity resulting from investments by owners and distributions to owners.

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The portion of profit or loss for the period, net of income taxes, which is attributable to the parent.

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Amount after tax of other comprehensive income (loss) attributable to parent entity.

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Amount, after tax and reclassification adjustment, of (increase) decrease in accumulated other comprehensive income for defined benefit plan.

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