Long-Term Debt (Subordinated Convertible Notes and Terms) (Details) - Subordinated Convertible Notes Due 2029		12 Months Ended
	Dec. 15, 2009 $ / shares shares	Dec. 31, 2017 $ / shares shares
Debt Instrument [Line Items]
Debt instrument, beginning date		Aug. 31, 2029
Conversion price per share | $ / shares	$ 36.75
Conversion, shares per $1,000 principal amount of notes	27.2109
Convertible, conversion ratio	0.000272	0.010816
Common stock covered under note hedges		11,686,075
Make-Whole
Debt Instrument [Line Items]
Common stock covered under note hedges		14,315,419
Any Calendar Quarted after March 31, 2010
Debt Instrument [Line Items]
Closing price as percent		130.00%
Consecutive trading days		30 days
Contingent, conversion price | $ / shares		$ 47.78
Any Calendar Quarted after March 31, 2010 | Minimum
Debt Instrument [Line Items]
Trading days		20 days
On or After November 15, 2019
Debt Instrument [Line Items]
Closing price as percent		150.00%
Consecutive trading days		30 days
On or After November 15, 2019 | Minimum
Debt Instrument [Line Items]
Trading days		20 days
During Any Five Business Days
Debt Instrument [Line Items]
Closing price as percent		98.00%
During Any Five Business Days | Minimum
Debt Instrument [Line Items]
Trading days		5 days