Consolidated Statements of Comprehensive Income (unaudited) (Parenthetical) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Other comprehensive (loss) income, net of tax:
Unrealized net holding (losses) gains arising during the period, pre-tax amounts	$ (15,454)	$ 836
Reclassification adjustment for an impairment write-down of equity security, pre-tax amounts	0	1,312
Unrealized gains on derivatives (cash flow hedges), pre-tax amounts	1,048	249
Reclassification of net unrealized (gains) losses on cash flow hedges to interest expense, pre-tax amounts	(359)	82
Amortization of unrealized net gains and losses related to the reclassification of available for sale investment securities to held to maturity, pre-tax amounts	188	238
Amortization of prior service cost and actuarial gains, pre-tax amounts	$ 295	$ 435