Net Income Per Share (Calculation Of Net Income Per Share) (Details) (USD $) In Thousands, except Per Share data, unless otherwise specified	3 Months Ended								12 Months Ended
	Dec. 31, 2011	Sep. 30, 2011	Jun. 30, 2011	Mar. 31, 2011	Dec. 31, 2010	Sep. 30, 2010	Jun. 30, 2010	Mar. 31, 2010	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2009
Calculation of Net Income Per Share [Line Items]
Net income	$ 42,624	$ 44,168	$ 36,425	$ 26,705	$ 24,790	$ 20,623	$ 12,181	$ 8,475	$ 149,922	$ 66,069	$ 37,263
Net income available to common stockholders									147,763	63,729	35,067
Basic weighted average shares									140,479	142,833	145,912
Basic net income per share	$ 0.30	$ 0.31	$ 0.25	$ 0.18	$ 0.17	$ 0.14	$ 0.08	$ 0.05	$ 1.05	$ 0.45	$ 0.24
Net income available to common stockholders - diluted	42,037	43,556	35,890	26,293	24,144	20,099	11,660	7,626	147,772	63,729	35,067
Dilutive effect of potential common shares									1,311	1,195	699
Diluted weighted average shares									141,790	144,028	146,611
Diluted net income per share	$ 0.30	$ 0.31	$ 0.25	$ 0.18	$ 0.17	$ 0.14	$ 0.08	$ 0.05	$ 1.04	$ 0.44	$ 0.24
Basic [Member]
Calculation of Net Income Per Share [Line Items]
Income allocated to participating securities									2,159	2,340	2,196
Diluted [Member]
Calculation of Net Income Per Share [Line Items]
Income allocated to participating securities									$ 2,150	$ 2,340	$ 2,196