Income Taxes (Details) - USD ($)	3 Months Ended	9 Months Ended		12 Months Ended
	Mar. 31, 2016	Sep. 30, 2015	Sep. 30, 2012	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Income Tax Examination [Line Items]
Number Of Years Of Tax Loss Carryback Period				2 years
Tax Adjustments, Settlements, and Unusual Provisions				$ 5,000,000	$ 17,000,000	$ 12,000,000	$ 15,000,000
Unrecognized Tax Benefits [Abstract]
Unrecognized tax benefit — Permanent tax positions	$ 20,500,000			20,100,000
Unrecognized tax benefit — Temporary tax positions	37,000,000			35,300,000
Total unrecognized tax benefit	57,500,000			55,400,000
NOL and tax credit carryforwards	(16,300,000)			(15,200,000)
Upper bound of decrease in unrecognized tax benefit that is reasonably possible	32,000,000
Amounts accrued for penalties related to unrecognized tax benefits	0			$ 0
Internal Revenue Service (IRS)
Tax Audits [Abstract]
Year(s) under examination		2012 and 2013	2010 and 2011
Year of carryback claim under examination			2009
Potential Tax Adjustments	$ 14,000,000
State Jurisdiction (Minnesota)
Tax Audits [Abstract]
Earliest year subject to examination	2009