Income Taxes (Details 3) - USD ($) $ in Thousands	Dec. 31, 2015	Dec. 31, 2014
Deferred tax assets:
General business credits		$ 2,186
Impairment losses on investments	$ 294	291
License fees capitalized for tax purposes	53,439	61,770
Nonqualified stock options	37,424	42,697
SERP	17,141	17,478
STAP awards	95,152	86,414
Other	27,074	29,086
Total deferred tax assets	230,524	239,922
Deferred tax liabilities:
Plant and equipment principally due to differences in depreciation	(26,461)	(30,758)
Other	(7,995)	(7,854)
Net deferred tax asset before valuation allowance	196,068	201,310
Valuation allowance	(3,392)	(2,981)
Net deferred tax assets	$ 192,676	$ 198,329