EPS Calculation (Details) (USD $) In Thousands, except 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
Numerator:
Net income	$ 70,564	$ 83,699	$ 79,286	$ 82,865	$ 61,581	$ 77,214	$ 48,290	$ 82,677	$ 316,414	$ 269,762	$ 268,189
Dividends declared on preferred stock									(8,160)	(8,160)	(8,160)
Dividends, DERs and undistributed earnings allocated to participating securities									(1,684)	(972)	(877)
Net income allocable to common stockholders - basic and diluted									$ 306,570	$ 260,630	$ 259,152
Denominator:
Weighted average common shares for basic earnings per share (in shares)									341,368,000	281,173,000	246,365,000
Add: Weighted average dilutive equity instruments (in shares)									259,000	70,000	59,000
Denominator for diluted earnings per share (in shares)									341,627,000	281,243,000	246,424,000
Basic and diluted EPS (in dollars per share)	$ 0.19	$ 0.23	$ 0.22	$ 0.27	$ 0.21	$ 0.27	$ 0.16	$ 0.29	$ 0.90	$ 0.93	$ 1.06
Anti-dilutive securities
Anti-dilutive securities excluded from diluted earnings per share calculations (in shares)									657,000
Stock options
Anti-dilutive securities
Anti-dilutive securities excluded from diluted earnings per share calculations (in shares)									477,000
Weighted average exercise price (in dollars per share)	$ 10.15								$ 10.15
Weighted average remaining contractual life (in years)	1.8								1.8
Restricted common stock
Anti-dilutive securities
Anti-dilutive securities excluded from diluted earnings per share calculations (in shares)									165,000
Weighted average grant date fair value (in dollars per share)	$ 8.18								$ 8.18
Restricted Stock Units
Anti-dilutive securities
Anti-dilutive securities excluded from diluted earnings per share calculations (in shares)									15,000
Weighted average grant date fair value (in dollars per share)	$ 5.63								$ 5.63