Disclosures About Fair Value of Assets and Liabilities - Additional Information (Details) (USD $)	3 Months Ended			9 Months Ended
	Sep. 30, 2014	Jun. 30, 2014 security	Sep. 30, 2013	Sep. 30, 2014	Sep. 30, 2013	Dec. 31, 2013
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Gain on sale of securities	$ 910,000			$ 2,335,000	$ 487,000
Number of securities remaining after sale		2
Investment amortized cost	1,173,850,000			1,173,850,000		1,097,226,000
Corporate obligations
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Number of securities sold		4
Number of securities owned		6
Amortized cost of sold securities		4,800,000
Gain on sale of securities		641,000
Investment amortized cost		1,500,000
Fair value of investments		$ 821,000