Restricted Stock Unit Activity (Detail) (Restricted Stock Unit (RSUs), USD $)	12 Months Ended
	Dec. 31, 2013	Dec. 31, 2012
Restricted Stock Unit (RSUs)
Number of Restricted Stock Units
Balance at beginning of period	207,339
Granted	217,216	210,891
Transferred to restricted	(192,672)
Forfeited	(12,672)	(3,552)
Balance at end of period	219,211	207,339
Weighted Average Grant Date Fair Value
Balance at beginning of period	$ 42.36
Granted	$ 41.63	$ 42.36
Transferred to restricted	$ 42.35
Forfeited	$ 42.42	$ 42.35
Balance at end of period	$ 41.64	$ 42.36