Income Taxes Income tax Expense (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended							12 Months Ended			15 Months Ended
	Dec. 31, 2012	Sep. 30, 2012	Jun. 30, 2012	Mar. 31, 2012	Dec. 31, 2011	Jun. 30, 2011	Mar. 31, 2011	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010	Sep. 30, 2012
Income Tax Expense (Benefit) [Abstract]
Current Income Tax Expense (Benefit)								$ 24,138	$ 24,736	$ 14,321
Deferred income taxes								(1,982)	(18,939)	(524)
Income tax expense/(benefit)	$ 4,837	$ 8,294	$ (2,629)	$ 11,654	$ 7,872	$ 2,539	$ 9,517	$ 22,156	$ 5,797	$ 13,797	$ (14,131)