Stock - Based Compensation - Summary of Accumulated Stock Units (Detail) - $ / shares	Dec. 31, 2015	Dec. 31, 2014
Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]
Accumulated stock units	66,376	60,859
Average price	$ 39.64	$ 37.41

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

No definition available.

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Data Type:	xbrli:sharesItemType
Balance Type:	na
Period Type:	instant