Financial Guarantees - Additional Information (Detail) - USD ($)	6 Months Ended
	Jun. 30, 2017	Dec. 31, 2016
Financial Guarantees [Line Items]
Term of standby letters of credit, years	1 year
Notional amount of standby letters of credit	$ 53,000,000	$ 51,700,000
Carrying value of letters of credit	300,000	300,000
Notional amount	810,000,000	$ 660,000,000
Interest Rate Swap [Member]
Financial Guarantees [Line Items]
Notional amount	$ 19,700,000