Employee Benefit Plans - Amounts in Accumulated Other Comprehensive Income on Consolidated Balance Sheets that have not been Recognized as Components of Net Periodic Pension Benefit Cost (Detail) (USD $) In Thousands, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Compensation and Retirement Disclosure [Abstract]
Net actuarial (loss)	$ (2,169)	$ (546)
Prior service credit	4,023	5,578
Total accumulated other comprehensive income	1,854	5,032	(13,058)
Income tax (expense)	(653)	(1,886)	5,128
Total accumulated other comprehensive income, net of tax	$ 1,201	$ 3,146	$ (7,930)