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Summary of Significant Accounting Policies (New Accounting Pronouncements and Changes in Accounting Principle) (Details) - USD ($)
$ in Thousands
 3 Months Ended
Mar. 31, 2017
Mar. 31, 2016
Jan. 01, 2017
New Accounting Pronouncements or Change in Accounting Principle [Line Items]      
Increase to net cash provided by operating activities $ 73,012 $ 78,645  
Corresponding offset to net cash used for financing activities $ 84,303 114,573  
Accounting Standards Update 2016-09 [Member]      
New Accounting Pronouncements or Change in Accounting Principle [Line Items]      
Increase to net cash provided by operating activities   624  
Corresponding offset to net cash used for financing activities   $ 624  
Increase to deferred tax assets     $ 913
Accounting Standards Update 2016-09 [Member] | Paid-in Capital [Member]      
New Accounting Pronouncements or Change in Accounting Principle [Line Items]      
Net cumulative effect adjustment     2,582
Accounting Standards Update 2016-09 [Member] | Retained Earnings [Member]      
New Accounting Pronouncements or Change in Accounting Principle [Line Items]      
Net cumulative effect adjustment     $ 1,669