CONSOLIDATED STATEMENTS OF SHAREHOLDERS' EQUITY (USD $) In Thousands, except Share data, unless otherwise specified	Common Shares	Additional Paid-in Capital	Cumulative Net Income	Cumulative Distributions	Unrealized Gain (Loss) on Investments	Total
Balance at Dec. 31, 2011	$ 1,626	$ 2,944,212	$ 907,937	$ (1,377,397)	$ (3,772)	$ 2,472,606
Increase (Decrease) in Shareholders' Equity
Comprehensive income			135,884		8,334	144,218
Distributions				(259,537)		(259,537)
Issuance of shares	138	286,914				287,052
Issuance of shares (in shares)	13,800,000
Share grants	1	2,228				2,229
Share grants (in shares)	107,554
Balance at Dec. 31, 2012	1,765	3,233,354	1,043,821	(1,636,934)	4,562	2,646,568
Balance (in shares) at Dec. 31, 2012	176,553,600
Increase (Decrease) in Shareholders' Equity
Comprehensive income			151,164		3,850	155,014
Distributions				(288,945)		(288,945)
Issuance of shares	115	261,698				261,813
Issuance of shares (in shares)	11,500,000
Share grants	1	2,538				2,539
Share grants (in shares)	114,043
Balance at Dec. 31, 2013	1,881	3,497,590	1,194,985	(1,925,879)	8,412	2,776,989
Balance (in shares) at Dec. 31, 2013	188,167,643					188,167,643
Increase (Decrease) in Shareholders' Equity
Comprehensive income			158,637		(5,083)	153,554
Distributions				(305,767)		(305,767)
Issuance of shares	156	325,455				325,611
Issuance of shares (in shares)	15,648,462
Share grants	2	2,018				2,020
Share grants (in shares)	94,200
Balance at Dec. 31, 2014	$ 2,039	$ 3,825,063	$ 1,353,622	$ (2,231,646)	$ 3,329	$ 2,952,407
Balance (in shares) at Dec. 31, 2014	203,910,305					203,910,305