Repurchase of Common Stock (Details) (USD $) In Thousands, unless otherwise specified			0 Months Ended			6 Months Ended	12 Months Ended
	Jun. 30, 2013	Dec. 31, 2012	Dec. 12, 2008 4.50% Notes and/or common stock [Member]	Oct. 13, 2008 4.50% Notes and/or common stock [Member]	Sep. 30, 2005 4.50% Notes and/or common stock [Member]	Jun. 30, 2013 4.50% Notes and/or common stock [Member]	Dec. 31, 2009 4.50% Notes and/or common stock [Member]
Equity, Class of Treasury Stock [Line Items]
Interest rate on notes excluded from earnings per share calculation (percent)				4.50%
Stock repurchase program, authorized amount			$ 30,000	$ 30,000	$ 9,864
Value of repurchased principal				35,920			14,076
Repurchased value of repurchased principal	3,019	3,019		28,112			11,696
Stock repurchase program, remaining authorized repurchase amount			$ 1,888			$ 18,304