Stock-Based Compensation - Performance-Based Restricted Stock Activity (Detail) - Performance-Based Restricted Stock [Member]	12 Months Ended
	Dec. 31, 2015 $ / shares shares
Schedule Of Restricted Stock Activity [Line Items]
Nonvested, Shares, Beginning Balance | shares	42,676
Performance-based Restricted Stock, Granted | shares	34,638
Performance-based Restricted Stock, Vested | shares	(35,679)
Performance-based Restricted Stock, Forfeited | shares	(12,538)
Nonvested, Shares, Ending Balance | shares	29,097
Nonvested, Weighted-Average Grant Price Per Share, Beginning Balance | $ / shares	$ 33.72
Weighted-Average Grant Price Per Share, Granted | $ / shares	43.89
Weighted-Average Grant Price Per Share, Vested | $ / shares	41.91
Weighted-Average Grant Price Per Share, Forfeited | $ / shares	38.12
Nonvested, Weighted-Average Grant Price Per Share, Ending Balance | $ / shares	$ 39.38