Cash Value of Life Insurance - Summary of Activity in Balance of Cash Value of Life Insurance (Detail) (USD $) In Thousands, unless otherwise specified	3 Months Ended
	Mar. 31, 2015 Policies Company Employees	Mar. 31, 2014 Company Employees Policies
Increase (Decrease) in Insurance Liabilities [Abstract]
Beginning balance	$ 92,337	$ 52,309
Increase in cash value of life insurance	675	397
Ending balance	93,012	52,706
End of period death benefit	$ 165,847	$ 94,999
Number of policies owned	189	133
Insurance companies used	14	6
Current and former employees and directors covered	60	36