Other Income (Expenses) (Tables)

12 Months Ended

Dec. 31, 2017

Other Income and Expenses [Abstract]

Principal components of other income (expense), net

The principal components of other income (expense), net are as follows (in thousands):

	Year Ended December 31,
	2017			2016			2015
Interest and investment income	$	548		$	72		$	90
Income tax expense	(214		)	(566		)	(295		)
Other non-operating income	—			126			108
Total other income (expense)	$	334		$	(368	)	$	(97	)