Investment Securities - 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
Schedule of Available for sale Securities and Held to maturity Securities [Line Items]
Carrying value of securities pledged as collateral	$ 415,652,000		$ 415,652,000		$ 373,533,000
Book value of securities sold under agreements to repurchase	128,222,000		128,222,000		126,900,000
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
Minimum
Schedule of Available for sale Securities and Held to maturity Securities [Line Items]
Spread over LIBOR			0.85%
Maximum
Schedule of Available for sale Securities and Held to maturity Securities [Line Items]
Spread over LIBOR			1.57%
Corporate obligations
Schedule of Available for sale Securities and Held to maturity Securities [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
Corporate obligations | Maximum
Schedule of Available for sale Securities and Held to maturity Securities [Line Items]
Percentage of fair value of investments (less than 1%)	1.00%		1.00%