Fair Values - Schedule of Details of Carrying Amount, Face Amount, and Fair Value of Financial Instruments (Detail) (USD $) In Thousands, unless otherwise specified	Sep. 30, 2014	Dec. 31, 2013
Financial assets
Loans receivable, net	$ 19,000	$ 40,700
Financial liabilities
Revolving repurchase facilities	1,669,406	863,622
Asset-specific repurchase agreements	226,961	245,731
Loan participations sold	447,977	90,000
Carrying Amount [Member]
Financial assets
Cash and cash equivalents	63,343	52,342
Restricted cash	10,855	10,096
Loans receivable, net	3,906,226	2,047,223
Financial liabilities
Revolving repurchase facilities	1,669,406	863,622
Asset-specific repurchase agreements	226,961	245,731
Loan participations sold	447,977	90,000
Convertible notes, net	161,259	159,524
Face Amount [Member]
Financial assets
Cash and cash equivalents	63,343	52,342
Restricted cash	10,855	10,096
Loans receivable, net	3,940,626	2,077,227
Financial liabilities
Revolving repurchase facilities	1,669,406	863,622
Asset-specific repurchase agreements	226,961	245,731
Loan participations sold	447,977	90,000
Convertible notes, net	172,500	172,500
Fair Value [Member]
Financial assets
Cash and cash equivalents	63,343	52,342
Restricted cash	10,855	10,096
Loans receivable, net	3,940,626	2,058,699
Financial liabilities
Revolving repurchase facilities	1,669,406	863,622
Asset-specific repurchase agreements	226,961	245,731
Loan participations sold	447,977	90,000
Convertible notes, net	$ 178,934	$ 181,772