CONDENSED CONSOLIDATED STATEMENTS OF SHAREHOLDERS' EQUITY (Unaudited) (USD $) In Thousands	Total	Non-Voting Common Stock [Member]	Voting Common Stock [Member]	Additional Paid-in Capital [Member]	Accumulated Other Comprehensive Income (Loss) [Member]	Retained Earnings [Member]
Balance at Dec. 31, 2012	$ 499,615	$ 1,246	$ 285	$ 295,582	$ (51)	$ 202,553
Balance, Shares at Dec. 31, 2012		12,565	2,853
Net (loss) earnings	8,838					8,838
Unrealized gain on short-term investments	19				19
Changes in pension plan assets and benefit obligations	(4)				(4)
Amortization of unearned stock-based compensation	400			400
Issuance of non-voting common stock (upon vesting of restricted stock units)	17	17
Issuance of non-voting common stock (upon vesting of restricted stock units), shares		4
Cancellation of restricted non-voting stock units for tax withholdings on vested shares	(65)	(6)		(59)
Cancellation of restricted non-voting stock units for tax withholdings on vested shares, shares		(1)
Issuance of voting common stock (upon vesting of restricted stock units)	9		9
Issuance of voting common stock (upon vesting of restricted stock units), shares			84
Cancellation of restricted voting stock units for tax withholdings on vested shares	(997)		(3)	(994)
Cancellation of restricted voting stock units for tax withholdings on vested shares, shares			(31)
Balance at Mar. 31, 2013	507,832	1,257	291	294,929	(36)	211,391
Balance, Shares at Mar. 31, 2013		12,568	2,906
Balance at Dec. 31, 2013	559,965	1,257	291	296,932	(24)	261,509
Balance, Shares at Dec. 31, 2013		12,568	2,906
Net (loss) earnings	(5,321)					(5,321)
Unrealized gain on short-term investments	8				8
Changes in pension plan assets and benefit obligations	(1)
Amortization of unearned stock-based compensation	688			688
Issuance of non-voting common stock (upon vesting of restricted stock units)	1	1
Issuance of non-voting common stock (upon vesting of restricted stock units), shares		11
Cancellation of restricted non-voting stock units for tax withholdings on vested shares	(176)			(176)
Cancellation of restricted non-voting stock units for tax withholdings on vested shares, shares		(4)
Balance at Mar. 31, 2014	$ 555,165	$ 1,258	$ 291	$ 297,444	$ (16)	$ 256,188
Balance, Shares at Mar. 31, 2014		12,575	2,906