Financial Statement Presentation - Effects of New Accounting Standards on Previously Reported Information (Details) - USD ($) $ in Thousands	3 Months Ended	6 Months Ended	9 Months Ended		12 Months Ended
	Mar. 31, 2016	Jun. 30, 2016	Sep. 30, 2017	Sep. 30, 2016	Dec. 31, 2016	Dec. 31, 2015
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Net Cash Provided by Operating Activities			$ 719,047	$ 257,705
Net Cash Provided by Financing Activities			$ (129,849)	463,115
Accounting Standards Update 2016-09
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Net Cash Provided by Operating Activities	$ 67,112	$ 152,290		257,705	$ 397,441	$ 749,598
Net Cash Provided by Financing Activities	565,751	492,428		463,115	453,805	223,296
As Reported | Accounting Standards Update 2016-09
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Net Cash Provided by Operating Activities	62,090	147,244		252,649	392,377	740,737
Net Cash Provided by Financing Activities	$ 570,773	$ 497,474		$ 468,171	$ 458,869	$ 232,157