Consolidated Statements of Comprehensive Income - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Statement of Comprehensive Income [Abstract]
Net income	$ 131,461	$ 175,722	$ 163,356
Other comprehensive income before income taxes
Reclassification of net change in unrealized (loss) gain	(21,270)	14,821	(105,274)
Reclassification of net losses realized and included in earnings	3,010	390	8,527
Valuation adjustment of employee benefit plans	(33,971)	(41,244)	82,653
Amortization of unrealized net loss (gain) on securities transferred to held to maturity	3,530	3,297	(6,371)
Other comprehensive loss before income taxes	(48,701)	(22,736)	(20,465)
Income tax benefit	(18,180)	(8,041)	(8,011)
Other comprehensive loss net of income taxes	(30,521)	(14,695)	(12,454)
Comprehensive income	$ 100,940	$ 161,027	$ 150,902