Condensed Consolidated Statements of Equity - USD ($) $ in Thousands	Total	Common Stock	Additional Paid-in Capital	Accumulated Deficit	Accumulated Other Comprehensive Income	Treasury Stock	Noncontrolling Interest
Beginning balance (in shares) at Dec. 31, 2016		23,125,000
Beginning balance at Dec. 31, 2016	$ 427,569	$ 23	$ 495,468	$ (173,231)	$ 6,661	$ (927)	$ 99,575
Beginning balance, treasury stock (in shares) at Dec. 31, 2016						55,000
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Stock-based compensation expense	898		717				181
Exercise of restricted stock units (in shares)		25,000
Exercise of restricted stock units	0
Withholding taxes paid on vested restricted stock units	(400)		(279)				(121)
Changes in ownership of noncontrolling interest	0		(411)				411
Acquisition of interests held by noncontrolling owners	0
Distribution of treasury stock to deferred compensation plan participants (in shares)
Distribution of treasury stock to deferred compensation plan participants	0
Distribution to noncontrolling interest	(26)						(26)
Purchases of treasury stock (in shares)						13,000
Purchases of treasury stock	(184)					$ (184)
Retirement of treasury stock (in shares)		(13,000)				(13,000)
Retirement of treasury stock	0		(184)			$ 184
Net income (loss)	6,034			4,643			1,391
Unrealized loss on investments, net of deferred income tax of $313 and reclassification adjustments of $740	(590)				(590)
Foreign currency translation	16				16
Ending balance (in shares) at Mar. 31, 2017		23,137,000
Ending balance at Mar. 31, 2017	433,317	$ 23	495,311	(168,588)	6,087	$ (927)	$ 101,411
Ending balance, treasury stock (in shares) at Mar. 31, 2017						55,000
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Reclassification of unrealized gain on investments to accumulated deficit	$ 17			561	(544)
Beginning balance (in shares) at Dec. 31, 2017	23,153,000	23,154,000
Beginning balance at Dec. 31, 2017	$ 207,163	$ 23	379,388	(172,767)	544	$ (25)
Beginning balance, treasury stock (in shares) at Dec. 31, 2017	1,000					1,000
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Stock-based compensation expense	$ 124		124
Purchases of treasury stock (in shares)						442,000
Purchases of treasury stock	(4,985)					$ (4,985)
Retirement of treasury stock (in shares)		(336,000)				(336,000)
Retirement of treasury stock	0		(3,776)			$ 3,776
Net income (loss)	$ (2,863)			(2,863)
Ending balance (in shares) at Mar. 31, 2018	22,818,000	22,818,000
Ending balance at Mar. 31, 2018	$ 199,456	$ 23	$ 375,736	$ (175,069)	$ 0	$ (1,234)
Ending balance, treasury stock (in shares) at Mar. 31, 2018	107,000					107,000