Loans Receivable - Principal Balance and Net Book Value of Loans Receivable Based on Internal Risk Ratings (Detail) (USD $) In Thousands, unless otherwise specified	3 Months Ended	12 Months Ended
	Mar. 31, 2014 SecurityLoan	Dec. 31, 2013 SecurityLoan
Accounts, Notes, Loans and Financing Receivable [Line Items]
Book value, net	$ 2,710,159	$ 2,047,223
Loans Receivable [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Number of Loans	41	31
Principal Balance	2,743,797	2,076,411
Book value, net	2,710,159	2,047,223
Risk Rating 1-3 [Member] | Loans Receivable [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Number of Loans	39	29
Principal Balance	2,706,249	2,038,863
Book value, net	2,683,159	2,020,223
Risk Rating 4-5 [Member] | Loans Receivable [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Number of Loans
Principal Balance
Book value, net
Risk Rating 6-8 [Member] | Loans Receivable [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Number of Loans	2	2
Principal Balance	37,548	37,548
Book value, net	$ 27,000	$ 27,000