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Stockholders' Equity - Discussion of Equity and Warrants (Details) - USD ($)
 3 Months Ended 6 Months Ended 9 Months Ended 12 Months Ended
Apr. 26, 2018
May 20, 2015
Dec. 31, 2018
Jun. 30, 2018
Sep. 30, 2018
Sep. 30, 2018
Dec. 31, 2018
Dec. 31, 2017
Dec. 31, 2016
Sep. 20, 2018
Dec. 31, 2015
Stockholders’ Equity and Regulatory Matters [Abstract]                      
Stockholders' equity     $ 1,903,211,000       $ 1,903,211,000 $ 1,928,255,000 $ 1,855,473,000   $ 938,095,000
Class of Warrant or Right [Line Items]                      
Adjustment to additional paid-in capital from convertible notes issued             $ 15,045,000 0 0    
Share repurchase program, authorized amount $ 100,000,000.0                 $ 50,000,000  
Common stock repurchased and recorded as treasury stock (in shares)     3,436,757     5,565,696 9,000,000        
Repurchase of treasury stock     $ 50,000,000   $ 100,000,000   $ 150,000,000        
Common Stock                      
Class of Warrant or Right [Line Items]                      
Number of shares repurchased under warrant to purchase   350,767                  
Payments for purchase of warrants   $ 1,200,000                  
Outstanding warrants     0       0        
Additional paid-in capital                      
Stockholders’ Equity and Regulatory Matters [Abstract]                      
Stockholders' equity     $ 1,423,405,000       $ 1,423,405,000 $ 1,405,014,000 $ 1,400,490,000   $ 541,596,000
Class of Warrant or Right [Line Items]                      
Adjustment to additional paid-in capital from convertible notes issued       $ 21,400,000     15,045,000        
Tax adjustment on equity component of convertible notes, reduction to additional paid-in capital       6,400,000              
Convertible Notes                      
Class of Warrant or Right [Line Items]                      
Equity component of convertible notes, net of taxes       21,900,000              
Issuance costs from convertible notes allocated to equity       $ 461,000              
Repurchase of treasury stock $ 76,000,000           $ 150,000,000