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Adoption of Accounting Pronouncements(Other Information) (Details) - USD ($)
$ / shares in Units, $ in Thousands
 12 Months Ended
Dec. 31, 2017
Dec. 31, 2016
Dec. 31, 2015
Share-based compensation expense income tax benefit $ (4,281) $ 0 $ 0
Accumulated other comprehensive income (loss) 20,170 (15,950)  
Available-for-sale Securities, Change in Net Unrealized Holding Gain (Loss), Net of Tax $ 10,000    
New Accounting Pronouncement or Change in Accounting Principle, Effect of Change on Diluted Earnings Per Share $ 0.17    
Proceeds from Equity Method Investment, Distribution $ 2,000 3,000  
Cash, Cash Equivalents, Restricted Cash and Restricted Cash Equivalents, Period Increase (Decrease), Including Exchange Rate Effect 7,000 25,000  
Equity Securities [Member]      
Accumulated other comprehensive income (loss) 25,000    
Available-for-sale Securities, Change in Net Unrealized Holding Gain (Loss) before Taxes 13,000    
National Flood Insurance Program [Member]      
Restricted cash $ 44,200 $ 36,900 $ 11,900