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Stock-Based Compensation Plans - Summarizes Transactions of SEUs (Detail) - Stock Equivalent Units [Member]
 3 Months Ended
Mar. 31, 2017
$ / shares
shares
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]  
Outstanding, Number of SEUs, Beginning balance | shares 279,815
Granted at discount, Number of SEUs | shares 174,249
Granted at market value, Number of SEUs | shares 5,530
Exercised, Number of SEUs | shares (29,989)
Forfeited, Number of SEUs | shares (11,775)
Outstanding, Number of SEUs, Ending balance | shares 417,830
Outstanding, Weighted Average Exercise Price, Beginning balance $ 3.77
Granted at discount, Weighted Average Exercise Price 0.00
Granted at market value, Weighted Average Exercise Price 70.60
Exercised, Weighted Average Exercise Price 6.21
Forfeited, Weighted Average Exercise Price 0.00
Outstanding, Weighted Average Exercise Price, Ending balance 3.02
Outstanding, Weighted Average Grant-Date Fair Value 33.40
Granted at discount, Weighted Average Grant-Date Fair Value 62.83
Granted at market value, Weighted Average Grant-Date Fair Value 16.84
Exercised, Weighted Average Grant-Date Fair Value 26.38
Forfeited, Weighted Average Grant-Date Fair Value 32.69
Outstanding, Weighted Average Grant-Date Fair Value $ 45.97