Consolidated Balance Sheets (Parenthetical) (USD $) In Thousands, except Share data, unless otherwise specified	Jun. 30, 2014	Dec. 31, 2013
Statement of Financial Position [Abstract]
Property, plant and equipment, accumulated depreciation (in dollars)	$ 2,224,728	$ 2,192,422
Preferred stock, authorized shares	10,000,000	10,000,000
Preferred stock, issued shares	0	0
Common stock, authorized shares	200,000,000	200,000,000
Common stock, issued shares	101,560,176	101,259,800
Common stock, outstanding shares	101,560,176	101,259,800