Consolidated Statements of Comprehensive Income - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2015	Jun. 30, 2014	Jun. 30, 2015	Jun. 30, 2014
Statement of Comprehensive Income [Abstract]
Net income	$ 31,431	$ 22,300	$ 50,738	$ 53,849
Net unrealized (loss) gain on securities available-for-sale:
Net unrealized (loss) gain on securities available-for-sale:	(2,748)	4,699	(755)	7,692
Reclassification adjustment for gain on sales of securities included in net income	(43)		(43)
Net unrealized (loss) gain on securities available-for-sale	(2,791)	4,699	(798)	7,692
Reclassification adjustment for net actuarial loss on pension plans and other postretirement benefits included in net income	417	161	886	296
Reclassification adjustment for prior service cost on pension plans and other postretirement benefits included in net income	27	31	56	61
Total other comprehensive (loss) income, net of tax	(2,347)	4,891	144	8,049
Comprehensive income	$ 29,084	$ 27,191	$ 50,882	$ 61,898