Employee Benefits - Components of Net Periodic Pension Cost and Other Changes in Plan Assets and Benefit (Detail) (USD $) In Thousands, unless otherwise specified	3 Months Ended		9 Months Ended
	Sep. 30, 2014	Sep. 30, 2013	Sep. 30, 2014	Sep. 30, 2013
Components of Net Periodic Pension Cost
Service cost—benefits earned during the period	$ 516	$ 659	$ 1,778	$ 2,075
Interest cost on projected benefit obligation	1,141	997	3,353	2,989
Expected return on plan assets	(1,710)	(1,526)	(5,180)	(4,656)
Amortization of prior service cost (credit)	(34)	(34)	(104)	(102)
Recognized net actuarial loss	287	642	705	1,818
Net Periodic Pension Expense	$ 200	$ 738	$ 552	$ 2,124