Divestiture and Discontinued Operations - Summary of financial information of discontinued operations (Details) - USD ($) $ in Thousands	12 Months Ended
Dec. 31, 2017	Dec. 31, 2016
Summarized financial results
(Provision for) benefit from income taxes	$ 100	$ 400
PAR Springer Miller Systems Inc
Assets
Other current assets	0	462
Assets of discontinued operations	0	462
Summarized financial results
Income (loss) from discontinued operations before income taxes	284	(1,131)
(Provision for) benefit from income taxes	(60)	411
Income (loss) from discontinued operations, net of taxes	$ 224	$ (720)

Amount before tax of income (loss) from a discontinued operation. Includes, but is not limited to, the income (loss) from operations during the phase-out period, gain (loss) on disposal, gain (loss) for reversal of write-down (write-down) to fair value, less cost to sell, and adjustments to a prior period gain (loss) on disposal.

Amount of tax expense (benefit) related to a discontinued operation. Includes, but is not limited to, tax expense (benefit) related to income (loss) from operations during the phase-out period, tax expense (benefit) related to gain (loss) on disposal, tax expense (benefit) related to gain (loss) for reversal of write-down (write-down) to fair value, less cost to sell, and tax expense (benefit) related to adjustments of a prior period gain (loss) on disposal.

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