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Stockholders' Equity - Nonvested Stock Activity (Detail)
6 Months Ended
Jun. 30, 2018
$ / shares
shares
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Number of Shares [Roll Forward]  
Nonvested shares outstanding, Number of Shares, Beginning Balance | shares 529,465
Granted, Number of Shares | shares 240,705
Vested, Number of Shares | shares (176,385)
Nonvested shares outstanding, Number of Shares, Ending Balance | shares 593,785
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Weighted Average Grant Date Fair Value [Abstract]  
Nonvested shares outstanding, Weighted average grant date fair value, Beginning Balance (in usd per share) | $ / shares $ 37.34
Granted, Weighted average grant date fair value (in usd per share) | $ / shares 62.35
Vested, Weighted average grant date fair value (in usd per share) | $ / shares 34.93
Nonvested shares outstanding, Weighted average grant date fair value, Ending Balance (in usd per share) | $ / shares $ 48.20
Share-based Compensation Arrangement by Share-based Payment Award, Options, Nonvested, Number of Shares [Roll Forward]  
Nonvested shares outstanding, Number of shares, Beginning Balance | shares 0
Granted, Number of shares | shares 0
Acquired, Number of shares | shares 270,710
Vested or exerccised, Number of shares | shares 10,727
Nonvested shares outstanding, Number of shares, Ending Balance | shares 259,983
Share-based Compensation Arrangement by Share-based Payment Award, Options, Nonvested, Weighted Average Grant Date Fair Value [Abstract]  
Nonvested shares outstanding, Weighted average grant date fair value, Beginning Balance (in usd per share) | $ / shares $ 0.00
Granted, Nonvested shares outstanding, Weighted average grant date fair value (in usd per share) | $ / shares 0.00
Acquired, Weighted average grant date fair value (in usd per share) | $ / shares 36.48
Vested or exercised, Weighted average grant date fair value (in usd per share) | $ / shares 29.08
Nonvested shares outstanding, Weighted average grant date fair value, Ending Balance (in usd per share) | $ / shares $ 36.66