Employee Benefit Plans - Schedule of Changes in Components of Accumulated Other Comprehensive Income (Detail) (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Compensation and Retirement Disclosure [Abstract]
Accumulated Other Comprehensive Income (Loss) Before Tax - Beginning Balance	$ 5,032	$ (13,058)
Net actuarial gain (loss)	(1,760)	17,566	621
Settlement gain	137	42	792
Actuarial (gains)/losses	0	2,037	2,718
Prior service costs/(credits)	(1,555)	(1,555)	(1,555)
Accumulated Other Comprehensive Income (Loss) Before Tax - Ending Balance	1,854	5,032	(13,058)
Income Tax Benefit (Expense) - Beginning Balance	(1,886)	5,128
Net actuarial gain (loss)	683	(6,811)	(242)
Settlement gain	(53)	(17)	(309)
Actuarial (gains)/losses	0	(790)	(1,062)
Prior service costs/(credits)	603	604
Income Tax Benefit (Expense) - Ending Balance	(653)	(1,886)	5,128
Accumulated Other Comprehensive Income (Loss) Net of Income Tax - Beginning Balance	3,146	(7,930)
Net actuarial gain (loss)	(1,077)	10,755	379
Settlement gain	84	25	483
Actuarial (gains)/losses	0	1,247	1,656
Prior service costs/(credits)	(952)	(951)	(948)
Accumulated Other Comprehensive Income (Loss) Net of Income Tax - Ending Balance	$ 1,201	$ 3,146	$ (7,930)