Common Stock (Performance Share Summary) (Details) (Performance Shares, USD $) In Thousands, except Per Share data, unless otherwise specified	12 Months Ended
	Dec. 31, 2012		Dec. 31, 2011		Dec. 31, 2010
Performance Shares
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Weighted average per share grant date fair value per share of performance shares awarded	$ 32.74		$ 23.45		$ 19.82
Fair value of performance shares vested	$ 1,193		$ 628		$ 663
Intrinsic value of performance shares vested	3,464		1,032		193
Compensation expense	170	[1]	1,573	[1]	988	[1]
Deferred tax expense related to compensation expense	$ 59		$ 551		$ 346

[1] Includes cumulative adjustments for forfeiture of performance share awards by certain executives.