Real Estate and Lending Activities - Schedule of Revenue from External Customers by Geographic Areas (Detail) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2017	Jun. 30, 2016	Jun. 30, 2017	Jun. 30, 2016
Investment And Revenue From External Customers By Geographic Area [Line Items]
Total Revenue	$ 166,807	$ 126,300	$ 323,204	$ 261,299
Revenue [Member] | Credit Concentration Risk [Member]
Investment And Revenue From External Customers By Geographic Area [Line Items]
Total Revenue			$ 323,204	$ 261,299
Percentage of Total Revenue			100.00%	100.00%
Revenue [Member] | Massachusetts [Member] | Credit Concentration Risk [Member]
Investment And Revenue From External Customers By Geographic Area [Line Items]
Total Revenue			$ 53,159
Percentage of Total Revenue			16.50%
Revenue [Member] | Texas [Member] | Credit Concentration Risk [Member]
Investment And Revenue From External Customers By Geographic Area [Line Items]
Total Revenue			$ 49,851	$ 48,256
Percentage of Total Revenue			15.40%	18.50%
Revenue [Member] | California [Member] | Credit Concentration Risk [Member]
Investment And Revenue From External Customers By Geographic Area [Line Items]
Total Revenue			$ 33,123	$ 33,187
Percentage of Total Revenue			10.30%	12.70%
Revenue [Member] | New Jersey [Member] | Credit Concentration Risk [Member]
Investment And Revenue From External Customers By Geographic Area [Line Items]
Total Revenue			$ 21,852	$ 18,243
Percentage of Total Revenue			6.80%	7.00%
Revenue [Member] | Arizona [Member] | Credit Concentration Risk [Member]
Investment And Revenue From External Customers By Geographic Area [Line Items]
Total Revenue			$ 15,542	$ 11,722
Percentage of Total Revenue			4.80%	4.50%
Revenue [Member] | All Other States [Member] | Credit Concentration Risk [Member]
Investment And Revenue From External Customers By Geographic Area [Line Items]
Total Revenue			$ 93,080	$ 99,931
Percentage of Total Revenue			28.70%	38.20%
Revenue [Member] | United States [Member] | Credit Concentration Risk [Member]
Investment And Revenue From External Customers By Geographic Area [Line Items]
Total Revenue			$ 266,607	$ 211,339
Percentage of Total Revenue			82.50%	80.90%
Revenue [Member] | Germany [Member] | Credit Concentration Risk [Member]
Investment And Revenue From External Customers By Geographic Area [Line Items]
Total Revenue			$ 54,576	$ 47,745
Percentage of Total Revenue			16.90%	18.30%
Revenue [Member] | United Kingdom, Italy, and Spain [Member] | Credit Concentration Risk [Member]
Investment And Revenue From External Customers By Geographic Area [Line Items]
Total Revenue			$ 2,021	$ 2,215
Percentage of Total Revenue			0.60%	0.80%
Revenue [Member] | International [Member] | Credit Concentration Risk [Member]
Investment And Revenue From External Customers By Geographic Area [Line Items]
Total Revenue			$ 56,597	$ 49,960
Percentage of Total Revenue			17.50%	19.10%