Investment and Mortgage-backed Securities - Continuous unrealized loss position (Details 4) (USD $) In Thousands, unless otherwise specified	Mar. 31, 2014 Security
Schedule Of Marketable Securities [Line Items]
Temporarily impaired securities, number of investments, less than 12 months	20
Temporarily impaired securities, fair value, less than 12 months	$ 73,761
Temporarily impaired securities, unrealized losses, less than 12 months	4,298
Temporarily impaired securities, number of investments, 12 months or longer	20
Temporarily impaired securities, fair value, 12 months or longer	63,558
Temporarily impaired securities, unrealized losses, 12 months or longer	4,290
Temporarily impaired securities, number of investments	40
Temporarily impaired securities, fair value	137,319
Temporarily impaired securities, unrealized losses	8,588
U.S. Government agency securities
Schedule Of Marketable Securities [Line Items]
Temporarily impaired securities, number of investments, less than 12 months	14
Temporarily impaired securities, fair value, less than 12 months	73,744
Temporarily impaired securities, unrealized losses, less than 12 months	4,297
Temporarily impaired securities, number of investments, 12 months or longer	12
Temporarily impaired securities, fair value, 12 months or longer	62,807
Temporarily impaired securities, unrealized losses, 12 months or longer	4,223
Temporarily impaired securities, number of investments	26
Temporarily impaired securities, fair value	136,551
Temporarily impaired securities, unrealized losses	8,520
Municipal obligations
Schedule Of Marketable Securities [Line Items]
Temporarily impaired securities, number of investments, less than 12 months
Temporarily impaired securities, fair value, less than 12 months
Temporarily impaired securities, unrealized losses, less than 12 months
Temporarily impaired securities, number of investments, 12 months or longer	1
Temporarily impaired securities, fair value, 12 months or longer	649
Temporarily impaired securities, unrealized losses, 12 months or longer	66
Temporarily impaired securities, number of investments	1
Temporarily impaired securities, fair value	649
Temporarily impaired securities, unrealized losses	66
Corporate stocks
Schedule Of Marketable Securities [Line Items]
Temporarily impaired securities, number of investments, less than 12 months
Temporarily impaired securities, fair value, less than 12 months
Temporarily impaired securities, unrealized losses, less than 12 months
Temporarily impaired securities, number of investments, 12 months or longer
Temporarily impaired securities, fair value, 12 months or longer
Temporarily impaired securities, unrealized losses, 12 months or longer
Temporarily impaired securities, number of investments
Temporarily impaired securities, fair value
Temporarily impaired securities, unrealized losses
Mortgage-backed securities
Schedule Of Marketable Securities [Line Items]
Temporarily impaired securities, number of investments, less than 12 months	6
Temporarily impaired securities, fair value, less than 12 months	17
Temporarily impaired securities, unrealized losses, less than 12 months	1
Temporarily impaired securities, number of investments, 12 months or longer	7
Temporarily impaired securities, fair value, 12 months or longer	102
Temporarily impaired securities, unrealized losses, 12 months or longer	1
Temporarily impaired securities, number of investments	13
Temporarily impaired securities, fair value	119
Temporarily impaired securities, unrealized losses	$ 2