Capital Stock - Additional Information (Details) (USD $)	1 Months Ended				1 Months Ended	12 Months Ended			12 Months Ended		1 Months Ended	12 Months Ended
	Mar. 30, 2012	Dec. 31, 2013	Dec. 31, 2012	Aug. 16, 2012	Mar. 30, 2012 Underwriters Overallotment Option	Dec. 31, 2013 Repurchase Program	Jun. 18, 2013 Repurchase Program	Dec. 31, 2012 2012 Program	Dec. 31, 2013 At The Market Transactions	Dec. 31, 2012 At The Market Transactions	Aug. 27, 2012 7.625% Series A Cumulative Redeemable Preferred Stock	Dec. 31, 2013 Common Stock Amount At The Market Transactions	Dec. 31, 2012 Common Stock Amount At The Market Transactions	Aug. 16, 2012 Prior To Amendment
Class Of Stock [Line Items]
Increased number of authorized preferred stock		25,000,000	25,000,000	25,000,000										10,000,000
Preferred stock, par value		$ 0.001	$ 0.001	$ 0.001							$ 0.001
Issuance of Common stock, shares	20,125,000				2,625,000						11,500,000	0	1,713,900
Shares issued pursuant to full exercise of underwriters' over allotment option											1,500,000
Liquidation preference per share											$ 25.00
Series A preferred stock dividend rate per year											7.625%
Annual dividend per share on the preferred stock											$ 1.90625
Total liquidation preference value		$ 287,500,000	$ 287,500,000								$ 287,500,000
Series A preferred stock, redemption date											Aug. 27, 2017
Common stock available for sale		200,000,000	200,000,000					10,000,000
Issuance of common stock net proceed	539,327								0	48,330,000
Sales commissions and fees												0	298
Common stock share authorized to repurchase							10,000,000
Stock repurchased during period, shares						2,485,447
Stock repurchased during period, value						$ 43,881,000
Issuance of Common stock, offering price	$ 26.81