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Employee Incentive and Retirement Plans - Black-Scholes Option Pricing Model to Estimate Fair Value of Stock Options Granted (Detail)
3 Months Ended 6 Months Ended
Jun. 30, 2015
Jun. 30, 2014
Jun. 30, 2015
Jun. 30, 2014
Disclosure of Compensation Related Costs, Share-based Payments [Abstract]        
Expected dividend yield 0.00% 0.00% 0.00% 0.00%
Weighted-average assumed stock price volatility 48.30% 52.40% 49.40% 54.30%
Weighted-average risk-free rate 1.72% 1.94% 1.61% 1.91%
Weighted-average expected life (in years) 6 years 3 months 6 years 3 months 5 days 6 years 3 months 6 years 4 months 15 days