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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

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