Real Estate and Lending Activities - Schedule of Gross Assets by Geographic Areas (Detail) - USD ($) $ in Thousands	6 Months Ended	12 Months Ended
	Jun. 30, 2016	Dec. 31, 2015
Investment And Revenue From External Customers By Geographic Area [Line Items]
Total Gross Assets	$ 5,117,933	$ 5,609,351
Assets, Total [Member] | Credit Concentration Risk [Member]
Investment And Revenue From External Customers By Geographic Area [Line Items]
Total Gross Assets	$ 5,422,395	$ 6,035,922
Percentage of Total Gross Assets	100.00%	100.00%
Assets, Total [Member] | Texas [Member] | Credit Concentration Risk [Member]
Investment And Revenue From External Customers By Geographic Area [Line Items]
Total Gross Assets	$ 920,959	$ 1,060,990
Percentage of Total Gross Assets	17.00%	17.60%
Assets, Total [Member] | California [Member] | Credit Concentration Risk [Member]
Investment And Revenue From External Customers By Geographic Area [Line Items]
Total Gross Assets	$ 547,079	$ 547,085
Percentage of Total Gross Assets	10.10%	9.10%
Assets, Total [Member] | All Other States [Member] | Credit Concentration Risk [Member]
Investment And Revenue From External Customers By Geographic Area [Line Items]
Total Gross Assets	$ 2,530,018	$ 3,047,204
Percentage of Total Gross Assets	46.60%	50.50%
Assets, Total [Member] | Other Domestic Assets [Member] | Credit Concentration Risk [Member]
Investment And Revenue From External Customers By Geographic Area [Line Items]
Total Gross Assets	$ 189,358	$ 177,317
Percentage of Total Gross Assets	3.50%	2.90%
Assets, Total [Member] | United States [Member] | Credit Concentration Risk [Member]
Investment And Revenue From External Customers By Geographic Area [Line Items]
Total Gross Assets	$ 4,187,414	$ 4,832,596
Percentage of Total Gross Assets	77.20%	80.10%
Assets, Total [Member] | Germany [Member] | Credit Concentration Risk [Member]
Investment And Revenue From External Customers By Geographic Area [Line Items]
Total Gross Assets	$ 1,054,368	$ 1,031,039
Percentage of Total Gross Assets	19.40%	17.10%
Assets, Total [Member] | United Kingdom, Italy, and Spain [Member] | Credit Concentration Risk [Member]
Investment And Revenue From External Customers By Geographic Area [Line Items]
Total Gross Assets	$ 156,630	$ 161,317
Percentage of Total Gross Assets	3.00%	2.70%
Assets, Total [Member] | Other International Assets [Member] | Credit Concentration Risk [Member]
Investment And Revenue From External Customers By Geographic Area [Line Items]
Total Gross Assets	$ 23,983	$ 10,970
Percentage of Total Gross Assets	0.40%	0.10%
Assets, Total [Member] | International [Member] | Credit Concentration Risk [Member]
Investment And Revenue From External Customers By Geographic Area [Line Items]
Total Gross Assets	$ 1,234,981	$ 1,203,326
Percentage of Total Gross Assets	22.80%	19.90%