Income Taxes (Details) (USD $) In Thousands, unless otherwise specified	6 Months Ended		12 Months Ended
	Jun. 30, 2012 Year certificates	Jun. 30, 2011	Dec. 31, 2011	Dec. 31, 2010 Year
Income Tax Disclosure [Abstract]
Effective tax rate	22.20%	25.70%	21.70%
Tax items related to prior year tax adjustments		$ 1,793
Tax holiday award period, extension granted				2
Tax holiday award period minimum	7
Tax holiday award period maximum	9
Number of awards scheduled to expire within one year	2