Earnings Per Share Level 4 (Details) (USD $) In Thousands, except Per Share data, unless otherwise specified	3 Months Ended																12 Months Ended
	Dec. 31, 2012		Sep. 30, 2012		Jun. 30, 2012		Mar. 31, 2012		Dec. 31, 2011		Sep. 30, 2011		Jun. 30, 2011		Mar. 31, 2011		Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Net Income (Loss) Attributable to Parent [Abstract]
Net income attributable to common stockholders	$ 26,383		$ 41,062		$ 37,076		$ 48,025		$ 44,550		$ 35,496		$ 26,093		$ 38,764		$ 152,546	$ 144,903	$ 126,417
After tax interest on convertible debt																	51	51	51
Net income — diluted																	$ 152,597	$ 144,954	$ 126,468
Weighted average shares (denominator):
Weighted average shares — basic																	(215,712)	(234,242)	(248,871)
Stock options																	3,233	2,306	1,610
Convertible debt																	121	121	121
Weighted average shares — diluted																	219,066	236,669	250,602
Net income attributable to common stockholders, basic	$ 0.12	[1]	$ 0.19	[1]	$ 0.17	[1]	$ 0.22	[1]	$ 0.20	[1]	$ 0.15	[1]	$ 0.11	[1]	$ 0.16	[1]	$ 0.71	$ 0.62	$ 0.51
Net income attributable to common stockholders, diluted	$ 0.12	[1]	$ 0.19	[1]	$ 0.17	[1]	$ 0.22	[1]	$ 0.20	[1]	$ 0.15	[1]	$ 0.11	[1]	$ 0.16	[1]	$ 0.70	$ 0.61	$ 0.50

[1] Net income per share is computed independently for each of the quarters presented. Therefore, the sum of the quarters’ net income per share may not equal the total computed for the year.