Quarterly Financial Data (Schedule of Quarterly Financial Information) (Details) (USD $) In Thousands, except Share data, unless otherwise specified	3 Months Ended								12 Months Ended
	Dec. 31, 2014	Sep. 30, 2014	Jun. 30, 2014	Mar. 31, 2014	Dec. 31, 2013	Sep. 30, 2013	Jun. 30, 2013	Mar. 31, 2013	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Quarterly Financial Data [Abstract]
Total revenues	$ 400,911	$ 393,955	$ 359,662	$ 336,756	$ 308,033	$ 324,797	$ 325,723	$ 304,351	$ 1,491,284	$ 1,262,904	$ 1,374,884
Segment profits	128,729	129,835	116,732	104,569	96,248	102,054	103,211	93,303	479,865	394,816	472,300
Net loss	$ (18,808)	$ 9,931	$ 2,443	$ (1,907)	$ (7,399)	$ (6,956)	$ (12,797)	$ (8,777)	$ (8,341)	$ (35,929)	$ 19,586
Basic	$ (0.46)	$ 0.24	$ 0.06	$ (0.05)	$ (0.18)	$ (0.17)	$ (0.32)	$ (0.22)	$ (0.20)	$ (0.89)	$ 0.48
Diluted	$ (0.46)	$ 0.24	$ 0.06	$ (0.05)	$ (0.18)	$ (0.17)	$ (0.32)	$ (0.22)	$ (0.20)	$ (0.89)	$ 0.47
Weighted average common shares outstanding, Basic	41,332,000	41,477,000	41,342,000	40,605,000	40,253,000	40,400,000	40,336,000	39,885,000	41,165,940	40,288,218	40,505,555
Weighted average common shares outstanding, Diluted	41,332,000	42,213,000	42,043,000	40,605,000	40,253,000	40,400,000	40,336,000	39,885,000	41,165,940	40,288,218	41,275,293