Stockholder's Equity (Narrative) (Details) (USD $)	0 Months Ended			1 Months Ended	12 Months Ended			1 Months Ended	0 Months Ended
	Dec. 09, 2014	Jul. 11, 2013	Feb. 19, 2013	May 22, 2014	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012	Feb. 28, 2010	May 07, 2013	May 09, 2014	Dec. 31, 2011
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Common stock, shares authorized					400,000,000	400,000,000
Common stock, par value					$ 0.01	$ 0.01
Preferred stock, shares					100,000,000	100,000,000
Preferred stock, par value					$ 0.01	$ 0.01
Preferred stock, shares issued					1,840,000	1,840,000
Preferred stock, shares outstanding					1,840,000	1,840,000
Public follow-on offering of common stock shares	9,775,000	5,750,000	5,750,000	8,050,000	42,869,463	24,990,120
Offering price per share of common stock	$ 19.60	$ 18.25	$ 16.60	$ 17.75
Shares sold to executive and senior officers and members of the board of directors		43,250	90,325
Net proceeds of the primary follow-on offering	$ 183,000,000	$ 99,900,000	$ 90,800,000	$ 136,500,000
Underwriting discount and offering costs	8,600,000	5,000,000	4,600,000	6,400,000
Issuance of common stock, net of issuance costs					319,481,000	190,748,000	55,049,000
Repayment on outstanding borrowings		6,500,000	65,400,000	100,000,000
Common stock, shares outstanding					42,869,463	24,990,120
Non-vested restricted stock awards					156,488	156,568
Compensation costs					1,100,000	900,000	700,000
Estimated net proceeds of the offering							44,551,000
Fair value of the restricted stock granted					1,000,000
Vesting period for the restricted stock					5 years
Total unrecognized compensation costs related to restricted stock issuances					1,800,000
Remaining weighted average period					3 years 2 months 12 days
Series A Preferred Stock [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Dividend rate					7.75%	7.75%
Redemption date of Series A Preferred Stock					Jul. 19, 2017
Redemption price of Series A Preferred Stock					$ 25.00
At-the-market Equity Offering Program [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Common stock aggregate offering price					100,000,000
LTIP [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Compensation costs					700,000	900,000	100,000
2010 Equity Incentive Plan [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Granted, Weighted Average Grant Date Fair Value								$ 14.20
Compensation costs						300,000
Amended and Restated 2010 Equity Incentive Plan [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Common stock, shares authorized					1,705,000
Granted, Weighted Average Grant Date Fair Value					$ 20.00
Compensation costs					$ 300,000
Remaining balance of shares available					1,304,840
Unresitricted Stock [Member] | 2010 Equity Incentive Plan [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Unrestricted common stock granted, shares									15,793
Granted, Weighted Average Grant Date Fair Value									$ 19.00
Unresitricted Stock [Member] | Amended and Restated 2010 Equity Incentive Plan [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Unrestricted common stock granted, shares										16,140
Granted, Weighted Average Grant Date Fair Value										$ 18.59
Restricted Stock [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Non-vested restricted stock awards					156,488	156,568	149,125				133,526
Unrestricted common stock granted, shares					51,146	48,891	47,536
Granted, Weighted Average Grant Date Fair Value					$ 18.38	$ 17.08	$ 14.20