EPS Calculation (Details) (USD $) In Thousands, except 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
Numerator:
Net income	$ 69,219	$ 78,141	$ 74,766	$ 84,713	$ 70,564	$ 83,699	$ 79,286	$ 82,865	$ 306,839	$ 316,414	$ 269,762
Dividends declared on preferred stock									(8,160)	(8,160)	(8,160)
Dividends, DERs and undistributed earnings allocated to participating securities									(1,517)	(1,684)	(972)
Net income allocable to common stockholders - basic and diluted									$ 297,162	$ 306,570	$ 260,630
Denominator:
Weighted average common shares for basic and diluted earnings per share									356,762,000	341,368,000	281,173,000
Basic and diluted EPS (in dollars per share)	$ 0.19	$ 0.21	$ 0.20	$ 0.23	$ 0.19	$ 0.23	$ 0.22	$ 0.27	$ 0.83	$ 0.90	$ 0.93
Anti-dilutive securities
Anti-dilutive securities excluded from diluted earnings per share calculations (in shares)									1,600,000
Stock options
Anti-dilutive securities
Anti-dilutive securities excluded from diluted earnings per share calculations (in shares)									427,000
Weighted average exercise price (in dollars per share)	$ 10.14								$ 10.14
Weighted average remaining contractual life									9 months 18 days
Restricted common stock
Anti-dilutive securities
Anti-dilutive securities excluded from diluted earnings per share calculations (in shares)									483,000
Weighted average grant date fair value (in dollars per share)	$ 7.74								$ 7.74
Restricted Stock Units
Anti-dilutive securities
Anti-dilutive securities excluded from diluted earnings per share calculations (in shares)									728,000
Weighted average grant date fair value (in dollars per share)	$ 6.43								$ 6.43