Notes Receivable - Additional Information (Detail) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2017 USD ($) Note	Jun. 30, 2016 USD ($)	Jun. 30, 2017 USD ($) Note	Jun. 30, 2016 USD ($)
Accounts, Notes, Loans and Financing Receivable [Line Items]
Interest income	$ 2,969	$ 3,008	$ 5,917	$ 6,151
National Bonds [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Number of notes receivable | Note	2		2
Interest income	$ 2,900	$ 3,000	$ 5,900	6,100
Payment received relating to notes receivables			$ 3,200	$ 3,300