Stock-based Compensation - Summary of Restricted Stock Units Activity (Detail) - 6 months ended Jun. 30, 2015 - Restricted Stock Units [Member] - $ / shares	Total
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of shares, Beginning Balance	179,936
Number of shares, Granted	78,747
Number of shares, Forfeited	(121)
Number of shares, Settled	(81,491)
Number of shares, Ending Balance	177,071
Weighted Average Grant Date Fair Value, Beginning Balance	$ 143.25
Weighted Average Grant Date Fair Value, Granted	139.30
Weighted Average Grant Date Fair Value, Forfeited	174.32
Weighted Average Grant Date Fair Value, Settled	103.28
Weighted Average Grant Date Fair Value, Ending Balance	$ 159.87