Financial Guarantees - Additional Information (Detail) - USD ($)	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015
Financial Guarantees [Line Items]
Term of standby letters of credit, years	1 year
Notional amount of standby letters of credit	$ 51,700,000	$ 62,600,000
Carrying value of letters of credit	300,000	400,000
Notional amount	660,000,000	$ 761,500,000
Interest Rate Swap [Member] | 2007 Interest Rate Swap Purchase [Member]
Financial Guarantees [Line Items]
Notional amount	6,800,000
Interest Rate Swap [Member] | 2014 Interest Rate Swap Purchase [Member]
Financial Guarantees [Line Items]
Notional amount	$ 9,900,000