Stock-Based Compensation and Stock Awards - Summary of PSA Activity (Detail) - Performance Unit Awards	12 Months Ended
	Dec. 31, 2017 $ / shares shares
Number of shares
Nonvested options, Beginning Balance (in shares) | shares	196,219
Granted (in shares) | shares	122,810
Vested (in shares) | shares	(52,444)
Forfeited (in shares) | shares	(2,311)
Nonvested options, Ending Balance (in shares) | shares	264,274
Weighted Average Grant Date Fair Value Per Unit
Nonvested Weighted Average Grant Date Fair Value, Beginning Balance (in dollars per share) | $ / shares	$ 78.42
Granted (in dollars per share) | $ / shares	54.64
Vested (in dollars per share) | $ / shares	126.84
Forfeited (in dollars per share) | $ / shares	126.84
Nonvested Weighted Average Grant Date Fair Value, Ending Balance (in dollars per share) | $ / shares	$ 59.97