Long-Term Debt (Narrative) (Details) (USD $) | 3 Months Ended | 0 Months Ended | 12 Months Ended | 0 Months Ended |
Mar. 31, 2015 | Mar. 31, 2014 | 15-May-13 | Dec. 31, 2014 | 10-May-13 |
pricing_tranch |
Debt Instrument [Line Items] | | | | | |
Long-term Debt | 196,470,000 | 630,256,000 | | $196,470,000 | |
Domestic And Multi-Currency Line Of Credit Up To $280,000 Due 2018 [Member] | | | | | |
Debt Instrument [Line Items] | | | | | |
Maximum borrowing capacity | | | | | 280,000,000 |
Commitment fee, percentage | 0.38% | | | | |
Weighted average interest rate | | 3.20% | | | |
Domestic And Multi-Currency Line Of Credit Up To $100,000 Due 2018 [Member] | | | | | |
Debt Instrument [Line Items] | | | | | |
Maximum borrowing capacity | | | | | 100,000,000 |
Number Of Pricing Tranches | | 3 | | | |
Variable Rate Senior Unsecured Note Due 2018 [Member] | | | | | |
Debt Instrument [Line Items] | | | | | |
Debt Instrument, Face Amount | | | | | 50,000,000 |
Debt instrument, maturity year | 2018 | | | | |
Long-term Debt | 0 | 31,250,000 | | 0 | |
Standby Letters Of Credit [Member] | | | | | |
Debt Instrument [Line Items] | | | | | |
Letter of credit facility, amount | 20,000,000 | | | | |
Line of Credit Facility, Amount Outstanding | 9,500,000 | | | | |
6.09% Series A Senior Unsecured Notes Due 2016 [Member] | | | | | |
Debt Instrument [Line Items] | | | | | |
Debt instrument, maturity year | 2016 | | | | |
Debt instrument, interest rate | 6.09% | | | | |
Long-term Debt | 0 | 21,000,000 | | 0 | |
7.26% Senior Unsecured Notes Due 2017 [Member] | | | | | |
Debt Instrument [Line Items] | | | | | |
Debt instrument, maturity year | 2017 | | | | |
Debt instrument, interest rate | 7.26% | | | | |
Long-term Debt | 0 | 15,000,000 | | 0 | |
6.00% Series A Senior Unsecured Notes Due 2019 [Member] | | | | | |
Debt Instrument [Line Items] | | | | | |
Debt instrument, maturity year | 2019 | | | | |
Debt instrument, interest rate | 6.00% | | | | |
Long-term Debt | 0 | 47,000,000 | | 0 | |
6.21%Series B Senior Unsecured Notes Due 2021 [Member] | | | | | |
Debt Instrument [Line Items] | | | | | |
Debt instrument, maturity year | 2021 | | | | |
Debt instrument, interest rate | 6.21% | | | | |
Long-term Debt | 0 | 18,182,000 | | 0 | |
6.58% Series B Senior Unsecured Notes Due 2022 [Member] | | | | | |
Debt Instrument [Line Items] | | | | | |
Debt instrument, maturity year | 2022 | | | | |
Debt instrument, interest rate | 6.58% | | | | |
Long-term Debt | 0 | 5,000,000 | | 0 | |
5.75% senior unsecured notes due 2018 | | | | | |
Debt Instrument [Line Items] | | | | | |
Debt Instrument, Face Amount | | | 300,000,000 | | |
Debt instrument, maturity year | 2018 | | | | |
Debt instrument, maturity date | | | 15-May-18 | | |
Debt Instrument, Issuance Date | | | 15-May-13 | | |
Debt instrument, interest rate | 5.75% | | 5.75% | | |
Note Redeem Rate | | | 100.00% | | |
Note Repurchase Rate | | | 101.00% | | |
Long-term Debt | 196,470,000 | 300,000,000 | | 196,470,000 | |
Ownership Percentage | 100.00% | | | | |
Debt Instrument, Repurchased Face Amount | | | | 103,500,000 | |
Repayments of Long-term Debt | | | | $107,200,000 | |
Minimum | Domestic And Multi-Currency Line Of Credit Up To $280,000 Due 2018 [Member] | | | | | |
Debt Instrument [Line Items] | | | | | |
Commitment fee, percentage | | | | | 0.25% |
Minimum | Domestic And Multi-Currency Line Of Credit Up To $100,000 Due 2018 [Member] | | | | | |
Debt Instrument [Line Items] | | | | | |
Debt instrument maturity days | | 1 day | | | |
Minimum | LIBOR [Member] | Domestic And Multi-Currency Line Of Credit Up To $280,000 Due 2018 [Member] | | | | | |
Debt Instrument [Line Items] | | | | | |
Debt instrument basis spread on variable rate | | | | | 2.00% |
Minimum | Agent's Base Rate [Member] | Domestic And Multi-Currency Line Of Credit Up To $280,000 Due 2018 [Member] | | | | | |
Debt Instrument [Line Items] | | | | | |
Debt instrument basis spread on variable rate | | | | | 0.50% |
Maximum | Domestic And Multi-Currency Line Of Credit Up To $280,000 Due 2018 [Member] | | | | | |
Debt Instrument [Line Items] | | | | | |
Commitment fee, percentage | | | | | 0.50% |
Maximum | Domestic And Multi-Currency Line Of Credit Up To $100,000 Due 2018 [Member] | | | | | |
Debt Instrument [Line Items] | | | | | |
Debt instrument maturity days | | 30 days | | | |
Maximum | LIBOR [Member] | Domestic And Multi-Currency Line Of Credit Up To $280,000 Due 2018 [Member] | | | | | |
Debt Instrument [Line Items] | | | | | |
Debt instrument basis spread on variable rate | | | | | 3.25% |
Maximum | Agent's Base Rate [Member] | Domestic And Multi-Currency Line Of Credit Up To $280,000 Due 2018 [Member] | | | | | |
Debt Instrument [Line Items] | | | | | |
Debt instrument basis spread on variable rate | | | | | 1.75% |