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Stockholders' Equity (Details)
6 Months Ended
Jun. 30, 2018
transaction
Nov. 30, 2017
USD ($)
Jun. 30, 2015
USD ($)
Common Class A [Member]      
Class of Stock [Line Items]      
Share repurchase program authorized amount     $ 150,000,000
ASR transaction accounted for as a treasury stock repurchase   $ 150,000,000  
Accelerated Share Repurchase Agreement [Member]      
Class of Stock [Line Items]      
Stock repurchase program, number of transactions | transaction 2