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Stock Options, Restricted Stock and Restricted Stock Units - RSU (Details) - Restricted stock and restricted stock units [Member] - $ / shares
1 Months Ended 3 Months Ended
Feb. 28, 2017
Mar. 31, 2018
Schedule of restricted stock and restricted stock units activity    
Beginning Balance, Number of shares or units   716,128
Grants, Number of shares or units 144,577 144,577
Vested shares, Number of shares or units   (140,852)
Forfeitures, Number of shares or units   (11,331)
Ending Balance, Number of shares or units   708,522
Beginning Balance, Weighted-average grant price   $ 99.65
Grants, Weighted-average grant price   90.99
Vested shares, Weighted-average grant price   58.99
Forfeitures, Weighted-average grant price   57.37
Ending Balance, Weighted-average grant price   $ 107.51