Summary of Significant Accounting Policies - Components of intangible assets (Details 8) (USD $) In Thousands, unless otherwise specified	6 Months Ended	12 Months Ended
	Jun. 30, 2013	Dec. 31, 2012
Amortizable Intangible Assets:
Gross Carrying Amount	$ 17,636	$ 17,903
Accumulated Amortization	4,920	4,698
Net Carrying Amount	12,716	13,205
Trade Name
Indefinite-lived Intangible Assets:
Indefinite-lived Intangible Assets, Gross Carrying amount	1,100	1,100
Customer Relationships
Amortizable Intangible Assets:
Gross Carrying Amount	16,811	16,811
Accumulated Amortization	4,510	4,085
Net Carrying Amount	12,301	12,726
Customer Relationships | Maximum
Amortizable Intangible Assets:
Amortization Periods	25 years	25 years
Customer Relationships | Minimum
Amortizable Intangible Assets:
Amortization Periods	15 years	15 years
Other Intangible Assets Including Contracts
Amortizable Intangible Assets:
Gross Carrying Amount	825	1,092
Accumulated Amortization	410	613
Net Carrying Amount	$ 415	$ 479
Other Intangible Assets Including Contracts | Maximum
Amortizable Intangible Assets:
Amortization Periods	30 years	30 years
Other Intangible Assets Including Contracts | Minimum
Amortizable Intangible Assets:
Amortization Periods	5 years	5 years