Statements of Changes in Shareholders' Equity (USD $) In Thousands	Total	Preferred Stock	Common Stock Amount	7.625% Series A Cumulative Redeemable Preferred Stock	7.625% Series A Cumulative Redeemable Preferred Stock Preferred Stock	Common Stock Amount	Common Stock Amount	Additional Paid-in Capital	Additional Paid-in Capital Common Stock Amount	Retained Earnings	Accumulated Other Comprehensive Income
Balance at Dec. 31, 2009	$ 931,713					$ 36		$ 770,232		$ 8,722	$ 152,723
Issuance of stock	271,373					10		271,363
Share based compensation expense	1,432							1,432
Dividends declared on common stock	(181,702)									(181,702)
Net income	169,500									169,500
Other comprehensive income	(46,832)										(46,832)
Balance at Dec. 31, 2010	1,145,484					46		1,043,027		(3,480)	105,891
Issuance of stock	860,602					31		860,571
Share based compensation expense	1,150							1,150
Dividends declared on common stock	(278,852)									(278,852)
Net income	284,373									284,373
Other comprehensive income	67,431										67,431
Balance at Dec. 31, 2011	2,080,188					77		1,904,748		2,041	173,322
Issuance of stock		278,252	587,657		278,252		22		587,635
Share based compensation expense	1,920							1,920
Dividends declared on preferred stock	(7,551)									(7,551)
Dividends declared on common stock	(306,379)									(306,379)
Net income	349,245									349,245
Other comprehensive income	89,532										89,532
Balance at Dec. 31, 2012	$ 3,072,864			$ 278,252		$ 99		$ 2,494,303		$ 37,356	$ 262,854