Stock - Based Compensation - Summary of Accumulated Stock Units (Detail) (USD $)	Dec. 31, 2014	Dec. 31, 2013
Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]
Accumulated stock units	60,859	56,380
Average price	$ 37.41	$ 35.31

Deferred compensation arrangement with individual accumulated stock units For deferred board fees.

No definition available.

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