Consolidated Statements of Comprehensive Income (Parenthetical) (USD $)	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Statement of Comprehensive Income [Abstract]
Net change in Unrealized gains (losses), tax expense (benefit)	$ 14,781,000	$ (19,478,000)	$ 9,090,000
Reclassification adjustment for gains, tax expense	393,000	1,336,000	8,142,000
Change in unfunded pension liability related to unrealized gain, prior service cost and transition obligation, tax expense	808,000	0	0
Other comprehensive income related to the transfer of available-for-sale securities to held-to-maturity, tax expense	2,300,000	2,300,000	2,300,000
Other comprehensive income related to the transfer of available-for-sale securities to held-to-maturity, net of tax expense	$ 1,300,000	$ 1,300,000	$ 1,300,000