Summary of Significant Accounting Policies (Details 4)	6 Months Ended	12 Months Ended
Jun. 30, 2013	Dec. 31, 2012 Restricted Stock Units Minimum	Dec. 31, 2011 Restricted Stock Units Minimum	Dec. 31, 2010 Restricted Stock Units Minimum	Dec. 31, 2012 Restricted Stock Units Maximum	Dec. 31, 2011 Restricted Stock Units Maximum	Dec. 31, 2010 Restricted Stock Units Maximum
Share based compensation
Forfeiture rate assumption for equity based awards granted in 2009 and prior years (as a percent)	0.00%
Vesting period of restricted share units (RSUs)		1 year	1 year	2 years	3 years	3 years	4 years
Period for measuring market condition of award				2 years			4 years

Period which an employee's right to exercise an award is no longer contingent on satisfaction of either a service condition, market condition or a performance condition, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 718

-SubTopic 10

-Section 50

-Paragraph 2

-Subparagraph (a)(1)

-URI http://asc.fasb.org/extlink&oid=6415400&loc=d3e5070-113901

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