Consolidated Statements of Comprehensive Income (Unaudited) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2017	Mar. 31, 2016
Statement of Comprehensive Income [Abstract]
Net income	$ 14,407	$ 18,565
Net unrealized (loss) gain on securities available-for-sale:
Net unrealized holding (loss) gain on securities arising during the period	(432)	4,036
Reclassification adjustment for gain on sales of securities included in net income	0	(51)
Net unrealized (loss) gain on securities available-for-sale	(432)	3,985
Reclassification adjustment for net actuarial loss on pension plans and other postretirement benefits included in net income	371	397
Reclassification adjustment for prior service cost on pension plans and other postretirement benefits included in net income	29	28
Total other comprehensive (loss) income, net of tax	(32)	4,410
Comprehensive income	$ 14,375	$ 22,975