Employee Benefits - Additional Information (Detail) (USD $)	3 Months Ended	6 Months Ended
	Mar. 31, 2013	Jun. 30, 2013
Compensation And Retirement Disclosure [Abstract]
Number of years service to participate in supplemental plan		1 year
Expected contribution to pension plan in current fiscal year		$ 1,800,000
Current fiscal year contribution to pension plan		900,000
Expected contribution to pension plan in remainder of current fiscal year		900,000
Additional amount contributed to pension plan to reduce variable annual premiums	$ 2,819,000