Consolidated Statements of Comprehensive Income (USD $) In Thousands, unless otherwise specified	3 Months Ended
	Mar. 31, 2015	Mar. 31, 2014
Statement of Comprehensive Income [Abstract]
Net income	$ 19,307	$ 31,549
Net unrealized (loss) gain on securities available-for-sale:
Net unrealized gain on securities available-for-sale arising during the period	1,993	2,993
Reclassification adjustment for net actuarial loss on pension plans and other postretirement benefits included in net income	469	135
Reclassification adjustment for prior service cost on pension plans and other postretirement benefits included in net income	29	30
Total other comprehensive income, net of tax	2,491	3,158
Comprehensive income	$ 21,798	$ 34,707