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Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 230
-SubTopic 10
-Section 45
-Paragraph 24
-URI http://asc.fasb.org/extlink&oid=98514028&loc=d3e3521-108585

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 230
-SubTopic 10
-Section 45
-Paragraph 28
-URI http://asc.fasb.org/extlink&oid=98514028&loc=d3e3602-108585

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-Publisher FASB
-Name Accounting Standards Codification
-Topic 230
-SubTopic 10
-Section 45
-Paragraph 25
-URI http://asc.fasb.org/extlink&oid=98514028&loc=d3e3536-108585

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Recent Accounting Pronouncements (Narrative) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015	Jan. 01, 2018
New Accounting Pronouncement, Early Adoption [Line Items]
Cumulative-effect adjustment from adoption of ASU 2016-09		$ 829
Increase to net cash provided by operating activities	$ 147,265	153,860	$ 147,276
Increase to net cash used in financing activities	$ (55,787)	481,563	(154,299)
Retained Earnings
New Accounting Pronouncement, Early Adoption [Line Items]
Cumulative-effect adjustment from adoption of ASU 2016-09		829
Accounting Standards Update 2016-09
New Accounting Pronouncement, Early Adoption [Line Items]
Increase to net cash provided by operating activities		8,200	700
Increase to net cash used in financing activities		8,200	$ 700
Accounting Standards Update 2016-09 \| Retained Earnings
New Accounting Pronouncement, Early Adoption [Line Items]
Cumulative-effect adjustment from adoption of ASU 2016-09		$ 800
Accounting Standards Update 2014-09 \| Minimum \| Scenario, Forecast
New Accounting Pronouncement, Early Adoption [Line Items]
Cumulative-effect adjustment from adoption of ASU 2016-09				$ 285,000
Accounting Standards Update 2014-09 \| Maximum \| Scenario, Forecast
New Accounting Pronouncement, Early Adoption [Line Items]
Cumulative-effect adjustment from adoption of ASU 2016-09				$ 295,000