Stockholders' Equity - Summary of Stock Option Activity under Stock Option Plan (Detail) - $ / shares	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2016	Dec. 31, 2015
Shares under option:
Outstanding at beginning of year, Amount	20,375
Forfeited, Amount	(9,050)
Exercised, Amount	(11,325)
Exercisable at end of year, Amount	0
Available to be granted at end of year, Amount	233,934	233,934	233,934
Outstanding at beginning of year, Weighted Average Exercise Price	$ 31.82
Forfeited, Weighted Average Exercise Price	31.83
Exercised, Weighted Average Exercise Price	31.81
Outstanding at end of year, Weighted Average Exercise Price	0
Exercisable at end of year, Weighted Average Exercise Price	$ 0