Debt Annual interest rates (Details)	Dec. 31, 2017	Jul. 14, 2016	Oct. 15, 2015	Jan. 05, 2015
Debt Instrument [Line Items]
Debt Instrument, Interest Rate, Stated Percentage		4.07%	10.25%	4.81%
Connecticut Statutory Trust I [Member]
Debt Instrument [Line Items]
Debt Instrument, Interest Rate, Stated Percentage	4.00%
Connecticut Statutory Trust II [Member]
Debt Instrument [Line Items]
Debt Instrument, Interest Rate, Stated Percentage	4.10%
Connecticut Statutory Trust III [Member]
Debt Instrument [Line Items]
Debt Instrument, Interest Rate, Stated Percentage	3.95%
Delaware Statutory Trust III [Member]
Debt Instrument [Line Items]
Debt Instrument, Interest Rate, Stated Percentage	4.20%
Delaware Statutory Trust IV [Member]
Debt Instrument [Line Items]
Debt Instrument, Interest Rate, Stated Percentage	3.85%
Delaware Statutory Trust VI [Member]
Debt Instrument [Line Items]
Debt Instrument, Interest Rate, Stated Percentage	4.00%