Transactions with Related Parties - Additional Information (Detail) (USD $)	0 Months Ended	6 Months Ended					6 Months Ended				6 Months Ended			1 Months Ended
	May 13, 2013	Jun. 30, 2013	Jun. 30, 2012	May 30, 2013	Dec. 31, 2012	May 31, 2013 Class A Common Stock [Member]	Jun. 30, 2013 Affiliate of Manager [Member]	May 13, 2013 Affiliate of Manager [Member]	Jun. 30, 2013 Affiliate of Manager [Member] Class A Common Stock [Member]	May 22, 2013 Affiliate of Manager [Member] Class A Common Stock [Member]	Jun. 30, 2013 Affiliate of our Manager [Member]	Jun. 30, 2013 W. R. Berkley Corporation [Member]	May 13, 2013 Blackstone [Member]	Dec. 20, 2012 Sale to Holdings III [Member]
Related Party Transaction Due From To Related Party [Line Items]
Class A common shares acquired by Holdings III, price per share														$ 20.00
Class A common shares acquired by Holdings III, shares		25,875,000												500,000
Accrued management fees payable							$ 920,000
Management fees paid to Manager							71,000
Preferred distributions payable to affiliate of our Manager											382,000
Payments of preferred distributions to affiliate of our Manager											2,300,000
Special servicing fees											651,000
Joint venture agreement date	May 13, 2013
Percentage of equity interest purchased	100.00%			100.00%				83.30%					16.70%
Joint venture agreement end date	May 30, 2013
Charge to noncontrolling interest from purchase of equity interests at fair value	193,000
Common stock, shares issued		28,802,000			2,927,000	25,875,000				1,960,784
Common stock, par value		$ 0.10			$ 0.10					$ 25.50
Common stock, shares outstanding percentage									8.50%
Aggregate amount of offering as stated in letter agreement, threshold												$ 30,000,000
Beneficially owned common stock and stock units (as a percent)												1.30%