Financial Instruments (Narrative) (Details) (USD $) In Thousands, unless otherwise specified																						12 Months Ended
	Jun. 30, 2012 6.25% Senior Notes [Member]	Jun. 30, 2012 6.5% Senior Notes [Member]	Jun. 30, 2012 8.25% Senior Notes [Member]	Dec. 31, 2012 Carrying Amount [Member] Fair value inputs, Level 2 [Member]	Dec. 31, 2011 Carrying Amount [Member] Fair value inputs, Level 2 [Member]	Dec. 31, 2011 Carrying Amount [Member] Interest Rate Swap [Member] Fair value inputs, Level 2 [Member]	Dec. 31, 2012 Carrying Amount [Member] 6.25% Senior Notes [Member] Fair value inputs, Level 2 [Member] Senior Notes [Member]	Dec. 31, 2011 Carrying Amount [Member] 6.25% Senior Notes [Member] Fair value inputs, Level 2 [Member] Senior Notes [Member]	Dec. 31, 2012 Carrying Amount [Member] 6.5% Senior Notes [Member] Fair value inputs, Level 2 [Member] Senior Notes [Member]	Dec. 31, 2011 Carrying Amount [Member] 6.5% Senior Notes [Member] Fair value inputs, Level 2 [Member] Senior Notes [Member]	Dec. 31, 2012 Carrying Amount [Member] 8.25% Senior Notes [Member] Fair value inputs, Level 2 [Member] Senior Notes [Member]	Dec. 31, 2011 Carrying Amount [Member] 8.25% Senior Notes [Member] Fair value inputs, Level 2 [Member] Senior Notes [Member]	Dec. 31, 2012 Fair Value [Member] Fair value inputs, Level 2 [Member]	Dec. 31, 2011 Fair Value [Member] Fair value inputs, Level 2 [Member]	Dec. 31, 2011 Fair Value [Member] Interest Rate Swap [Member] Fair value inputs, Level 2 [Member]	Dec. 31, 2012 Fair Value [Member] 6.25% Senior Notes [Member] Fair value inputs, Level 2 [Member] Senior Notes [Member]	Dec. 31, 2011 Fair Value [Member] 6.25% Senior Notes [Member] Fair value inputs, Level 2 [Member] Senior Notes [Member]	Dec. 31, 2012 Fair Value [Member] 6.5% Senior Notes [Member] Fair value inputs, Level 2 [Member] Senior Notes [Member]	Dec. 31, 2011 Fair Value [Member] 6.5% Senior Notes [Member] Fair value inputs, Level 2 [Member] Senior Notes [Member]	Dec. 31, 2012 Fair Value [Member] 8.25% Senior Notes [Member] Fair value inputs, Level 2 [Member] Senior Notes [Member]	Dec. 31, 2011 Fair Value [Member] 8.25% Senior Notes [Member] Fair value inputs, Level 2 [Member] Senior Notes [Member]	Dec. 31, 2012 Accumulated Other Comprehensive Income (Loss) [Member] Cash Flow Hedging [Member] Interest Rate Swap [Member]	Dec. 31, 2011 Accumulated Other Comprehensive Income (Loss) [Member] Cash Flow Hedging [Member] Interest Rate Swap [Member]	Dec. 31, 2012 Other Liabilities [Member] Cash Flow Hedging [Member] Interest Rate Swap [Member]	Dec. 31, 2011 Other Liabilities [Member] Cash Flow Hedging [Member] Interest Rate Swap [Member]
Debt Instrument [Line Items]
Senior notes, carrying value				$ 443,673	$ 332,988		$ 0	$ 184,895	$ 295,275	$ 0	$ 148,398	$ 148,093	$ 484,125	$ 344,350		$ 0	$ 186,850	$ 321,000	$ 0	$ 163,125	$ 157,500
Unrealized Gain (Loss) on Interest Rate Cash Flow Hedges, Pretax, Accumulated Other Comprehensive Income (Loss)																						(3,430)	(520)
Derivative Financial Instruments, Liabilities, Fair Value Disclosure																								3,430	520
Interest rate swap						520									520
Liabilities, Fair Value Disclosure				$ 447,103	$ 333,508								$ 487,555	$ 344,870
Stated interest rate, senior notes	6.25%	6.50%	8.25%