Other Comprehensive Income (Details 2) - USD ($) $ in Thousands		3 Months Ended
		Mar. 31, 2017	Mar. 31, 2016
Net gain on securities transactions		$ 23,137	$ 21,180
Tax expense		(7,388)	(6,896)
Unrealized gains and losses on available-for-sale securities
Net of tax		0	139
Net retirement plan actuarial (gain) loss
Total before tax	[1],[2]	(357)	(343)
Net retirement plan prior service cost
Total before tax	[1],[2]	(23)	(30)
Employee Benefit Plans
Total before tax	[1]	(380)	(373)
Tax benefit	[1]	152	149
Net of tax	[1]	(228)	(224)
Amount Reclassified from Accumulated Other Comprehensive Income | Unrealized gains and losses on available-for-sale securities
Net gain on securities transactions	[1]	0	232
Tax expense	[1]	0	(93)
Net of tax	[1]	$ 0	$ 139

[1] Amounts in parentheses indicated debits in income statement.

[2] The accumulated other comprehensive (loss) income components are included in the computation of net periodic benefit cost (See Note 10 - “Employee Benefit Plan”).