Consolidated Statements of Comprehensive Income (unaudited) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2017	Jun. 30, 2016	Jun. 30, 2017	Jun. 30, 2016
Consolidated Statements of Comprehensive Income (unaudited) [Abstract]
Net income	$ 21,359	$ 19,909	$ 41,638	$ 38,800
Other comprehensive income, net of tax:
Unrealized net holding gains arising during the period (pre-tax amounts of $2,528, $3,730, $3,364 and $16,941)	1,562	2,278	2,059	10,350
Reclassification adjustment for net (gains) related to securities available for sale included in net income (pre-tax amounts of $2, $1, $2 and $30)	(1)	0	(1)	(19)
Reclassification adjustment for an impairment write-down of equity security (pre-tax amounts of $-, $-, $1,312 and $-)	0	0	811	0
Unrealized gains on derivatives (cash flow hedges) (pre-tax amounts of ($434), ($62), ($104) and ($62))	(268)	(38)	(64)	(38)
Amortization of unrealized net gains related to the reclassification of available for sale investment securities to held to maturity (pre-tax amounts of $225, $280, $463 and $576)	139	171	286	352
Pension and other benefits:
Amortization of prior service cost and actuarial loss (pre-tax amounts of $435, $513, $870 and $1,024)	269	313	538	626
Total other comprehensive income	1,701	2,724	3,629	11,271
Comprehensive income	$ 23,060	$ 22,633	$ 45,267	$ 50,071