Investments - Additional Information (Details)	1 Months Ended	6 Months Ended
	Nov. 30, 2007 USD ($) issuer institution company	Jun. 30, 2015 USD ($) Investment	Jun. 30, 2014 USD ($)	Dec. 31, 2014 USD ($)
Schedule of Available-for-sale Securities [Line Items]
Aggregate fair market value of securities pledged as collateral		$ 3,800,000		$ 3,600,000
Impairment credit losses on available-for-sale securities		0	$ 0
Portion of other-than-temporary impairment losses recognized in other comprehensive loss		585,000		433,000
Amortized Cost		57,982,000		62,276,000
Estimated Fair Value		56,396,000		60,926,000
Gross Unrealized Loss		$ 1,636,000		1,421,000
Asset-backed security [Member]
Schedule of Available-for-sale Securities [Line Items]
Number of securities | Investment		1
Trust preferred securities, number of issuers | issuer	56
Trust preferred securities, number of U.S. depository institutions | institution	45
Trust preferred securities, number of insurance companies | company	11
Available for sale security purchased, face value	$ 3,000,000.0
Available for sale security purchased, price as percentage of face amount	95.21%
Available for sale security purchased, price paid	$ 2,900,000
Trust preferred securities issued, value	$ 363,000,000
Basis points over 3 months LIBOR	0.60%
Amortized Cost		$ 2,050,000		2,083,000
Estimated Fair Value		1,465,000		1,650,000
Gross Unrealized Loss		585,000		$ 433,000
Available-for-sale securities, default experienced		$ 42,500,000
Percentage of default to total current collateral		12.50%
Security payment deferrals		$ 12,000,000
Percentage of payment deferrals to total current collateral		3.50%
Excess subordination		$ 52,500,000