Quarterly report pursuant to Section 13 or 15(d)

Stock Compensation - Summary of Nonvested Shares Related to Equity Incentive Plans (Detail)

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Stock Compensation - Summary of Nonvested Shares Related to Equity Incentive Plans (Detail) - 6 months ended Jun. 30, 2015 - $ / shares
Total
Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]  
Nonvested, Shares, Beginning of Period 1,263,833
Granted, Shares 7,500
Vested, Shares (153,500)
Nonvested, Shares, End of Period 1,117,833
Nonvested, Weighted Average Grant-Date Fair Value, Beginning of Period $ 43.38
Granted, Weighted Average Grant-Date Fair Value 68.01
Vested, Weighted Average Grant-Date Fair Value 29.02
Nonvested, Weighted Average Grant-Date Fair Value, End of Period $ 45.52