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	1,565		1,334				231
Exercise of restricted stock units (in shares)		62,000
Exercise of restricted stock units	0
Withholding taxes paid on vested restricted stock units	(832)		(711)				(121)
Changes in ownership of noncontrolling interest	0		(465)				465
Acquisition of interests held by noncontrolling owners	0
Distribution of treasury stock to deferred compensation plan participants (in shares)						(54,000)
Distribution of treasury stock to deferred compensation plan participants	796		(106)			$ 902
Distribution to noncontrolling interest	(26)						(26)
Purchases of treasury stock (in shares)						47,000
Purchases of treasury stock	(690)					$ (690)
Retirement of treasury stock (in shares)		(47,000)				(47,000)
Retirement of treasury stock	0		(690)			$ 690
Net income (loss)	9,015			6,219			2,796
Unrealized loss on investments, net of deferred income tax of $3,176 and reclassification adjustments of $9,179	(5,899)				(5,899)
Foreign currency translation	25				25
Ending balance (in shares) at Jun. 30, 2017		23,140,000
Ending balance at Jun. 30, 2017	431,523	$ 23	494,830	(167,012)	787	$ (25)	102,920
Ending balance, treasury stock (in shares) at Jun. 30, 2017						1,000
Beginning balance at Mar. 31, 2017					6,087
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income (loss)	2,980
Ending balance (in shares) at Jun. 30, 2017		23,140,000
Ending balance at Jun. 30, 2017	431,523	$ 23	494,830	(167,012)	787	$ (25)	$ 102,920
Ending balance, treasury stock (in shares) at Jun. 30, 2017						1,000
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Reclassification of unrealized gain on investments to accumulated deficit	$ 16			560	(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	$ 300		300
Exercise of restricted stock units (in shares)		23,000
Exercise of restricted stock units	0
Purchases of treasury stock (in shares)						1,155,000
Purchases of treasury stock	(12,945)					$ (12,945)
Retirement of treasury stock (in shares)		(1,155,000)				(1,155,000)
Retirement of treasury stock	0	$ (1)	(12,944)			$ 12,945
Net income (loss)	$ 1,440			1,440
Ending balance (in shares) at Jun. 30, 2018	22,022,000	22,022,000
Ending balance at Jun. 30, 2018	$ 195,974	$ 22	366,744	(170,767)	0	$ (25)
Ending balance, treasury stock (in shares) at Jun. 30, 2018	1,000					1,000
Beginning balance at Mar. 31, 2018
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income (loss)	$ 4,302
Ending balance (in shares) at Jun. 30, 2018	22,022,000	22,022,000
Ending balance at Jun. 30, 2018	$ 195,974	$ 22	$ 366,744	$ (170,767)	$ 0	$ (25)
Ending balance, treasury stock (in shares) at Jun. 30, 2018	1,000					1,000