Changes in Accumulated Other Comprehensive Income (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended
	Mar. 31, 2015	Mar. 31, 2014
Changes in accumulated other comprehensive income by component
Balance at the beginning of the period	$ (24,370)	$ (11,900)
Other comprehensive income before reclassification adjustments	2,996	5,847
Amounts reclassified from accumulated other comprehensive income	151	(2,042)
Other comprehensive income	3,147	3,805
Balance at the end of the period	(21,223)	(8,095)
Income tax expense related to compensation and employee benefits	(140)	75
Unrealized gains and losses on securities available-for-sale
Changes in accumulated other comprehensive income by component
Balance at the beginning of the period	3,461	(3,233)
Other comprehensive income before reclassification adjustments	2,952	5,596
Amounts reclassified from accumulated other comprehensive income	(68)	(1,904)
Other comprehensive income	2,884	3,692
Balance at the end of the period	6,345	459
Realized gains (losses) on securities, net of tax	111	3,122
Tax on realized gains on securities	(43)	(1,218)
Change in fair value of interest rate swaps
Changes in accumulated other comprehensive income by component
Balance at the beginning of the period	(4,078)	(5,224)
Other comprehensive income before reclassification adjustments	44	251
Other comprehensive income	44	251
Balance at the end of the period	(4,034)	(4,973)
Change in defined benefit pension plans
Changes in accumulated other comprehensive income by component
Balance at the beginning of the period	(23,753)	(3,443)
Amounts reclassified from accumulated other comprehensive income	219	(138)
Other comprehensive income	219	(138)
Balance at the end of the period	(23,534)	(3,581)
Amortization of prior service cost (compensation and employee benefits)	581	581
Amortization of net loss (compensation and employee benefits)	(940)	(368)
Income tax expense related to compensation and employee benefits	$ 140	$ (75)