Basis of Presentation Follow On Offering (Details) (USD $) In Thousands, except Per Share data, unless otherwise specified	12 Months Ended		3 Months Ended
	Dec. 31, 2012	Dec. 31, 2010	Mar. 31, 2012 Follow On Offering of the Company [Member] Follow On Offering Q1 2012 [Member]	Mar. 31, 2012 Follow On Offering of Underwriter to Public [Member] Follow On Offering Q1 2012 [Member]	Sep. 30, 2012 Follow On Offering of Selling Shareholders [Member] Follow On Offering Q3 2012 [Member]	Mar. 31, 2012 Follow On Offering of Affiliate (Shinsei) [Member] Follow On Offering Q1 2012 [Member]	Sep. 30, 2012 Follow On Offering of Affiliate (Shinsei) [Member] Follow On Offering Q3 2012 [Member]	Mar. 31, 2012 Transactions with Vestar Capital Partners [Member] Follow On Offering Q1 2012 [Member]	Sep. 30, 2012 Transactions with Vestar Capital Partners [Member] Follow On Offering Q3 2012 [Member]
Follow On Offering [Line Items]
Issuance of Class A common stock for follow-on offering, shares	3,707		3,707
Stock Issued During Period, Value Per Share, New Issues			$ 13.38
Stock Issued During Period, Value, New Issues, Gross			$ 49,606
Stock Issued During Period, Value Per Share, Underwriter to Public				$ 13.75		$ 13.75
Stock Issued During Period, Value, Underwriter to Public				50,978		20,178
Issuance of Class A common stock for follow-on offering, value	49,244	(3)	49,244
Redemption of New Class A Units, shares	(4,407)		(4,407)					(2,185)
Redemption of New Class A Units, value per unit			13.38					13.38
Redemption of New Class A Units, value	58,972		58,972					29,231
Stock Sold by Affiliate, Shares					3,083	1,468	1,205		1,878
Stock Sold by Affiliates, Value Per Share					$ 13.25	$ 13.38
Stock Sold by Affiliates, Value						$ 19,635