Debt (Senior Notes) (Details) - Senior notes $ in Millions	Dec. 31, 2018 USD ($)
Debt Instrument [Line Items]
Aggregate unamortized premium	$ 28.3
2021 Senior Notes
Debt Instrument [Line Items]
Interest rate	6.75%
2025 Senior Notes
Debt Instrument [Line Items]
Interest rate	6.875%

Amount, after accumulated amortization, of debt premium.

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 835
-SubTopic 30
-Section 55
-Paragraph 8
-URI http://asc.fasb.org/extlink&oid=114775985&loc=d3e28878-108400

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 835
-SubTopic 30
-Section 45
-Paragraph 1A
-URI http://asc.fasb.org/extlink&oid=114775744&loc=d3e28541-108399

Name:	us-gaap_DebtInstrumentUnamortizedPremium
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant