| Summary of Significant Accounting Policies- Derivative Financial Instruments (Details) (Interest rate swap instruments, USD $) In Thousands, unless otherwise specified | 12 Months Ended | 1 Months Ended | 1 Months Ended | |||||
|---|---|---|---|---|---|---|---|---|
| Dec. 31, 2007
 contract | Dec. 31, 2007
 Interest Rate Swap Contract 1 | Dec. 31, 2007
 Interest Rate Swap Contract 2 | Mar. 31, 2010
 Interest Rate Swap Contract 3 | Jul. 31, 2011
 Interest Rate Swap Contract 4 | Oct. 31, 2012
 Interest Rate Swap Contract 5
 swap | Sep. 30, 2013
 Interest Rate Swap Contract 5 | Oct. 31, 2012
 Interest Rate Swap Contract 6
 swap | |
| Derivative [Line Items] | ||||||||
| Number of instruments held (contracts) | 2 | 2 | 2 | |||||
| Term of interest rate swap contract | 15 years | 14 years | 5 years | 8 years | 8 years | |||
| Initial notional amount of interest rate swaps | $ 13,081 | $ 3,256 | $ 27,900 | $ 38,571 | $ 16,750 | $ 25,377 | ||
| Interest rate swaps, variable to fixed interest rates (percent) | 5.40% | 5.30% | 6.99% | 1.965% | 1.71% | 3.70% | ||
| Future increase in notional amount | $ 42,247 | |||||||