Earnings Per Share (Details) (USD $) In Thousands, except Share data, unless otherwise specified	3 Months Ended		9 Months Ended
	Sep. 30, 2014	Sep. 30, 2013	Sep. 30, 2014	Sep. 30, 2013
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Antidilutive Securities Excluded from Computation of Earnings Per Share, Amount	142	1,376	1,431	1,742
Net Income (Loss) Attributable to Parent [Abstract]
Net income attributable to common stockholders	$ 17,651	$ 26,779	$ 84,675	$ 118,015
After tax interest on convertible debt	0	13	38	38
Net income — diluted	$ 17,651	$ 26,792	$ 84,713	$ 118,053
Weighted average shares (denominator):
Weighted average shares — basic	(210,820,000)	(211,954,000)	(212,009,000)	(211,721,000)
Stock options	2,190,000	4,295,000	3,235,000	4,035,000
Convertible debt	0	121,000	121,000	121,000
Weighted average shares — diluted	213,010,000	216,370,000	215,365,000	215,877,000
Net income attributable to common stockholders, basic	$ 0.08	$ 0.13	$ 0.40	$ 0.56
Net income attributable to common stockholders, diluted	$ 0.08	$ 0.12	$ 0.39	$ 0.55
Equity Option [Member]
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Antidilutive Securities Excluded from Computation of Earnings Per Share, Amount	21	1,376	1,431	1,742
Antidilutive Convertible Debentures [Member]
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Antidilutive Securities Excluded from Computation of Earnings Per Share, Amount	121	0	0	0