Consolidated Statements of Comprehensive Income (unaudited) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2016	Sep. 30, 2015	Sep. 30, 2016	Sep. 30, 2015
Statement of Comprehensive Income [Abstract]
Net income	$ 34,709	$ 37,669	$ 100,808	$ 84,731
Change in securities available-for-sale:
Unrealized holding gains for the period	3,428	14,509	33,956	6,581
Reclassification adjustment for securities gains realized in income	(1,647)	(861)	(4,609)	(4,056)
Income tax effect	(693)	(5,021)	(10,670)	(1,101)
Unrealized gains on available-for-sale securities	1,088	8,627	18,677	1,424
Change in securities held-to-maturity:
Amortization of fair value for securities held-to-maturity previously recognized into accumulated other comprehensive income	439	455	1,370	1,222
Income tax effect	(150)	(155)	(468)	(236)
Changes from securities held-to-maturity	289	300	902	986
Cash flow hedges:
Net unrealized derivative gains (losses) on cash flow hedges	3,133	(10,278)	(12,480)	(12,349)
Reclassification adjustment for losses realized in net income	1,865	902	4,723	1,527
Income tax effect	(1,899)	3,563	2,948	4,112
Changes from cash flow hedges	3,099	(5,813)	(4,809)	(6,710)
Defined benefit pension plans:
Amortization of net loss recognized in income	503	917	1,933	2,380
Income tax effect	(191)	(349)	(735)	(905)
Changes from defined benefit pension plans	312	568	1,198	1,475
Other comprehensive income (loss), net of tax	4,788	3,682	15,968	(2,825)
Comprehensive income	$ 39,497	$ 41,351	$ 116,776	$ 81,906