Consolidated Statements of Changes in Shareholders' Equity - USD ($) $ in Thousands	Total	Common Stock	Capital In Excess of Par Value	Retained Earnings
Beginning balances at Dec. 31, 2013	$ 2,173,392	$ 9,659	$ 445,470	$ 1,718,263
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income (loss)	136,276	0	0	136,276
Activity in employee compensation plans	22,726	73	22,653	0
Ending balances at Dec. 31, 2014	2,332,394	9,732	468,123	1,854,539
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income (loss)	(1,037,361)	0	0	(1,037,361)
Activity in employee compensation plans	18,547	99	18,448	0
Ending balances at Dec. 31, 2015	1,313,580	9,831	486,571	817,178
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income (loss)	(135,624)	0	0	(135,624)
Activity in employee compensation plans	16,114	185	15,929	0
Ending balances at Dec. 31, 2016	$ 1,194,070	$ 10,016	$ 502,500	$ 681,554