Disclosures About Fair Value of Assets and Liabilities - Additional Information (Details) (USD $)	3 Months Ended		6 Months Ended
	Jun. 30, 2014 security	Jun. 30, 2013	Jun. 30, 2014	Jun. 30, 2013	Dec. 31, 2013
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Gain on sale of securities	$ 844,000	$ 239,000	$ 1,425,000	$ 487,000
Number of securities remaining after sale	2
Investment amortized cost	1,197,609,000		1,197,609,000		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		4,800,000
Gain on sale of securities	641,000
Investment amortized cost	1,500,000		1,500,000
Fair value of investments	$ 764,000		$ 764,000