Related-Party Transactions (Details) (USD $) In Thousands, unless otherwise specified	12 Months Ended	1 Months Ended
Dec. 31, 2011	Dec. 31, 2010	May 31, 2010 AMP and ACOF
Related-party transactions
Annual management fee prior to the initial public offer (IPO)			$ 1,250
Minimum percentage of collective common stock holding required for continuation of agreement			5.00%
One-time fee to be paid upon consummation of IPO to eliminate annual management fee and a transaction fee			5,800
Management fees and related expense recognized	$ 46	$ 6,383

Expenses recognized resulting from transactions (excluding transactions that are eliminated in consolidated or combined financial statements) with related party.

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

-Publisher FASB

-Name Statement of Financial Accounting Standard (FAS)

-Number 57

-Paragraph 2

-Subparagraph c

-LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy.

Reference 2: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 850

-SubTopic 10

-Section 50

-Paragraph 1

-Subparagraph (c)

-URI http://asc.fasb.org/extlink&oid=6457730&loc=d3e39549-107864

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Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration