Stockholders' Equity - Narrative (Details)											12 Months Ended			33 Months Ended
	Apr. 22, 2015 USD ($) $ / shares shares	Nov. 26, 2014 USD ($)	[1]	Apr. 07, 2014 USD ($)	[1]	Jan. 10, 2014 USD ($)	[1]	Jun. 04, 2013 USD ($) $ / shares shares	May. 03, 2013 USD ($)	[1]	Dec. 31, 2015 USD ($) director quarter $ / shares shares	Dec. 31, 2014 USD ($) $ / shares shares	Dec. 31, 2013 USD ($) $ / shares	Mar. 20, 2015 USD ($) $ / shares shares	Jun. 11, 2012 USD ($)
Class of Stock [Line Items]
Preferred stock, shares authorized (in shares) | shares											200,000,000	200,000,000
Preferred stock, par value (in dollars per share)											$ 0.01	$ 0.01
Preferred stock, shares issued (in shares) | shares											6,600,000	6,600,000
Preferred stock, shares outstanding (in shares) | shares											3,000,000	3,000,000
Preferred stock issuance, net | $											$ 86,862,000	$ 0	$ 72,397,000
Common stock dividend per share (in dollars per share)											$ 1.02	$ 1.08	$ 1.08
Common stock, par value (in dollars per share)											$ 0.01	$ 0.01
Net proceeds | $		$ 110,784,000		$ 109,916,000		$ 75,846,000			$ 94,434,000		$ 31,799,000	$ 296,546,000	$ 100,207,000
Ordinary Income
Class of Stock [Line Items]
Common stock dividend per share (in dollars per share)											$ 0.399764	$ 0.61	$ 0.81
Capital Gain Distribution
Class of Stock [Line Items]
Common stock dividend per share (in dollars per share)											0.065284	0.35
Return of Capital
Class of Stock [Line Items]
Common stock dividend per share (in dollars per share)											$ 0.554952	$ 0.12	$ 0.27
Equity Distribution Agreements
Class of Stock [Line Items]
Stock issued (in shares) | shares											2,789,439
Common stock subscriptions (up to) | $														$ 75,000,000
Common stock, par value (in dollars per share)														$ 0.01
Share price (in dollars per share)											$ 7.91
Net proceeds | $											$ 21,600,000
Common stock reserved for future issuance | $											$ 52,900,000
Prior Equity Distribution Agreement
Class of Stock [Line Items]
Stock issued (in shares) | shares											1,326,676			2,153,989
Common stock subscriptions (up to) | $															$ 25,000,000
Share price (in dollars per share)											$ 7.89			$ 7.63
Net proceeds | $											$ 10,300,000			$ 16,100,000
Series B and C Preferred Stock
Class of Stock [Line Items]
Minimum number of quarters without dividends that result in voting rights | quarter											6
Number of additional directors elected | director											2
Preferred stock, percentage of stockholders required for term changes											66.67%
Series B Preferred Stock
Class of Stock [Line Items]
Preferred stock, shares authorized (in shares) | shares											6,000,000	3,450,000
Preferred stock, par value (in dollars per share)								$ 0.01			$ 0.01	$ 0.01
Preferred stock, shares issued (in shares) | shares											3,000,000	3,000,000
Preferred stock, shares outstanding (in shares) | shares											3,000,000	3,000,000
Stock issued (in shares) | shares								3,000,000
Preferred stock, Series B cumulative redeemable, dividend rate (as a percent)								7.75%			7.75%	7.75%
Preferred stock, liquidation preference (in dollars per share)								$ 25			$ 25	$ 25
Preferred stock issuance, net | $								$ 72,400,000
Preferred stock, redemption price per share											$ 25.00
Preferred stock, redemption term											120 days
Series C Preferred Stock
Class of Stock [Line Items]
Preferred stock, shares authorized (in shares) | shares											4,140,000	0
Preferred stock, par value (in dollars per share)	$ 0.01										$ 0.01	$ 0
Preferred stock, shares issued (in shares) | shares	3,600,000										3,600,000	0
Preferred stock, shares outstanding (in shares) | shares											3,600,000	0
Preferred stock, Series B cumulative redeemable, dividend rate (as a percent)	7.875%										7.875%	0.00%
Preferred stock, liquidation preference (in dollars per share)	$ 25										$ 25	$ 0
Preferred stock issuance, net | $	$ 86,900,000

[1] Proceeds are net of underwriting costs and offering expenses paid by the Company.