Borrowings - Additional Information (Detail) - USD ($) $ in Thousands		3 Months Ended	9 Months Ended
	Oct. 24, 2014	Sep. 30, 2015	Sep. 30, 2015	Feb. 23, 2015	Dec. 31, 2014
Debt Instrument [Line Items]
Short-term borrowings		$ 10,000	$ 10,000
Additional borrowings during period			30,000
Repayments of borrowings			10,000
Revolving Credit Facility [Member]
Debt Instrument [Line Items]
Revolving credit facility	$ 50,000	$ 70,000	$ 70,000		$ 50,000
Term of revolving credit facility	5 years
Option to increase additional credit facility	$ 50,000			$ 50,000
Credit facility expiration date			Oct. 24, 2019
Interest rate during the period		1.56%	1.56%
Unamortized deferred finance cost		$ 392	$ 392		$ 460
Short-term borrowings		$ 10,000	10,000
Additional borrowings during period			30,000
Repayments of borrowings			$ 10,000