Condensed Consolidated Statements of Shareholders' Equity - USD ($) shares in Thousands, $ in Thousands	Voting Common Stock [Member] Common Stock [Member]	Nonvoting Common Stock [Member] Common Stock [Member]	Paid-In Capital [Member]	Treasury Stock [Member]	Retained Earnings [Member]	Accumulated Other Comprehensive Loss [Member]	Total
Balance at Dec. 31, 2015	$ 216	$ 95	$ 1,020,129	$ (9,592)	$ (873,660)	$ (28,698)	$ 108,490
Balance, shares at Dec. 31, 2015	21,582	9,506		154
Net income (loss)					47,200
Other comprehensive income (loss)						14,862
Comprehensive income (loss)							62,062
Adjustment to tax benefit associated with stock-based compensation			(141)				(141)
Balance at Dec. 31, 2016	$ 216	$ 95	1,019,988	$ (9,592)	(826,460)	(13,836)	170,411
Balance, shares at Dec. 31, 2016	21,582	9,506		154
Net income (loss)					93,719		93,719
Other comprehensive income (loss)						(15,215)	(15,215)
Comprehensive income (loss)							78,504
Cumulative effect adjustment attributable to previously unrecognized excess tax benefits on stock-based compensation					4,741		4,741
Balance at Sep. 30, 2017	$ 216	$ 95	$ 1,019,988	$ (9,592)	$ (728,000)	$ (29,051)	$ 253,656
Balance, shares at Sep. 30, 2017	21,582	9,506		154