Consolidated Statements of Changes in Shareholders' Equity - USD ($) $ in Thousands	Total	Common Stock	Capital In Excess of Par Value	Accumulated Other Comprehensive Income	Retained Earnings
Beginning balances at Dec. 31, 2012	$ 1,974,301	$ 9,594	$ 423,603	$ 7,587	$ 1,533,517
Comprehensive income:
Net income (loss)	184,746	0	0	0	184,746
Other comprehensive loss, net of tax	(7,587)	0	0	(7,587)	0
Comprehensive income (loss)	177,159
Activity in employee compensation plans	21,932	65	21,867	0	0
Ending balances at Dec. 31, 2013	2,173,392	9,659	445,470	0	1,718,263
Comprehensive income:
Net income (loss)	136,276	0	0	0	136,276
Other comprehensive loss, net of tax				0
Comprehensive income (loss)	136,276
Activity in employee compensation plans	22,726	73	22,653	0	0
Ending balances at Dec. 31, 2014	2,332,394	9,732	468,123	0	1,854,539
Comprehensive income:
Net income (loss)	(1,037,361)	0	0	0	(1,037,361)
Other comprehensive loss, net of tax				0
Comprehensive income (loss)	(1,037,361)
Activity in employee compensation plans	18,547	99	18,448	0	0
Ending balances at Dec. 31, 2015	$ 1,313,580	$ 9,831	$ 486,571	$ 0	$ 817,178