Financing Agreements - Redemption Price Expressed as Percentage of Principal Amount (Details)	Dec. 31, 2018
Senior Notes Due September 2023 [Member] | Debt Instrument, Redemption, Period One [Member]
Debt Instrument [Line Items]
Debt redemption price	102.00%
Senior Notes Due September 2023 [Member] | Debt Instrument, Redemption, Period Two [Member]
Debt Instrument [Line Items]
Debt redemption price	101.00%
Senior Notes Due September 2023 [Member] | Debt Instrument, Redemption, Period Three [Member]
Debt Instrument [Line Items]
Debt redemption price	100.00%
Senior Notes Due September 2023 [Member] | Debt Instrument, Redemption, Period Four [Member]
Debt Instrument [Line Items]
Debt redemption price	100.00%
Senior Notes Due December 2024 [Member] | Debt Instrument, Redemption, Period One [Member]
Debt Instrument [Line Items]
Debt redemption price	102.75%
Senior Notes Due December 2024 [Member] | Debt Instrument, Redemption, Period Two [Member]
Debt Instrument [Line Items]
Debt redemption price	101.833%
Senior Notes Due December 2024 [Member] | Debt Instrument, Redemption, Period Three [Member]
Debt Instrument [Line Items]
Debt redemption price	100.917%
Senior Notes Due December 2024 [Member] | Debt Instrument, Redemption, Period Four [Member]
Debt Instrument [Line Items]
Debt redemption price	100.00%
Senior Notes Due December 2024 [Member] | Debt Instrument, Redemption, Period Five [Member]
Debt Instrument [Line Items]
Debt redemption price	100.00%
Senior Notes Due April 2025 [Member] | Debt Instrument, Redemption, Period One [Member]
Debt Instrument [Line Items]
Debt redemption price	105.75%
Senior Notes Due April 2025 [Member] | Debt Instrument, Redemption, Period Two [Member]
Debt Instrument [Line Items]
Debt redemption price	100.00%
Senior Notes Due April 2025 [Member] | Debt Instrument, Redemption, Period Three [Member]
Debt Instrument [Line Items]
Debt redemption price	104.313%
Senior Notes Due April 2025 [Member] | Debt Instrument, Redemption, Period Four [Member]
Debt Instrument [Line Items]
Debt redemption price	102.875%
Senior Notes Due April 2025 [Member] | Debt Instrument, Redemption, Period Five [Member]
Debt Instrument [Line Items]
Debt redemption price	101.438%
Senior Notes Due April 2025 [Member] | Debt Instrument, Redemption, Period Six [Member]
Debt Instrument [Line Items]
Debt redemption price	100.00%
Senior Notes Due April 2025 [Member] | Debt Instrument, Redemption, Period Seven [Member]
Debt Instrument [Line Items]
Debt redemption price	100.00%
Senior Notes Due June 2026 [Member] | Debt Instrument, Redemption, Period One [Member]
Debt Instrument [Line Items]
Debt redemption price	106.50%
Senior Notes Due June 2026 [Member] | Debt Instrument, Redemption, Period Two [Member]
Debt Instrument [Line Items]
Debt redemption price	100.00%
Senior Notes Due June 2026 [Member] | Debt Instrument, Redemption, Period Three [Member]
Debt Instrument [Line Items]
Debt redemption price	103.25%
Senior Notes Due June 2026 [Member] | Debt Instrument, Redemption, Period Four [Member]
Debt Instrument [Line Items]
Debt redemption price	102.167%
Senior Notes Due June 2026 [Member] | Debt Instrument, Redemption, Period Five [Member]
Debt Instrument [Line Items]
Debt redemption price	101.083%
Senior Notes Due June 2026 [Member] | Debt Instrument, Redemption, Period Six [Member]
Debt Instrument [Line Items]
Debt redemption price	100.00%
Senior Notes Due June 2026 [Member] | Debt Instrument, Redemption, Period Seven [Member]
Debt Instrument [Line Items]
Debt redemption price	100.00%