Commitments and Contingencies - Additional Information (Detail)		12 Months Ended
	Dec. 31, 2016 USD ($) Loans Directors	Dec. 31, 2016 USD ($) Loans Installments	Dec. 31, 2015 USD ($)
Commitments And Contingencies [Line Items]
Commitments expiration period		4 years
Number of loans receivable | Loans	58	58
Percentage of compensation paid in cash	40.00%
Percentage of compensation in the form of deferred stock units	60.00%
Number of board of directors | Directors	8
Number of independent directors entitled to annual compensation | Directors	5
Number of equal quarterly installments | Installments		4
Loans Receivable [Member]
Commitments And Contingencies [Line Items]
Unfunded loan commitments	$ 882,472,000	$ 882,472,000	$ 700,658,000
Five Independent Board of Directors [Member]
Commitments And Contingencies [Line Items]
Annual cash compensation	125,000
Three Board of Directors [Member]
Commitments And Contingencies [Line Items]
Annual cash compensation	125,000
Chairperson of Audit Committee [Member]
Commitments And Contingencies [Line Items]
Annual cash compensation	$ 12,000