Deferred Compensation Plan (Details) (USD $)	3 Months Ended	12 Months Ended
	Mar. 31, 2016	Dec. 31, 2013		Dec. 31, 2012	Dec. 31, 2011	Oct. 31, 2013	Aug. 01, 2013	Apr. 30, 2013	Feb. 21, 2014 Subordinated Debt [Member]	Jan. 22, 2014 Subordinated Debt [Member]	Oct. 18, 2013 Subordinated Debt [Member]	Aug. 01, 2013 Subordinated Debt [Member]	Mar. 08, 2013 Subordinated Debt [Member]	Dec. 21, 2012 Subordinated Debt [Member]	Mar. 10, 2010 Subordinated Debt [Member]	Dec. 31, 2013 2014 [Member]	Dec. 31, 2013 2015 through 2017 [Member]
Deferred Compensation Arrangement with Individual, Excluding Share-based Payments and Postretirement Benefits [Line Items]
Debt Instrument, Repurchased Face Amount									$ 20,000,000	$ 30,000,000	$ 155,000,000	$ 324,000,000	$ 50,000,000	$ 100,000,000	$ 28,500,000
Charge for payment of RDU Plan cash retention pool		7,500,000	[1]
Second RDU Cash Retention Payment	7,500,000
Redemption premium added to debt face amount, RDU plan		1,400,000
RDU plan cash retention pool							15,000,000
RDU Plan, Units Authorized for Issuance		28,500
RDU Plan, Units Outstanding		28,500
Deferred Compensation Arrangement with Individual, Requisite Service Period		P3Y0M0D
RDU Plan, Distributions Paid						1,300,000		1,700,000
RDU Plan, Compensation Expense		16,800,000		8,400,000	8,100,000
RDU Plan, unrecognized compensation expense																9,000,000	7,000,000
RDU Plan, Liability		$ 21,800,000		$ 15,500,000

[1] See Note 12 for additional discussion of this transaction