Accumulated Other Comprehensive Income (Loss) - Changes in Accumulated Other Comprehensive Income (Loss) (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2017	Mar. 31, 2016
Pre-tax Amount
Balance	$ (145,472)	$ (84,722)
Other comprehensive income	2,176	54,353
Balance	(143,296)	(30,369)
Income Tax Benefit (Expense)
Balance	57,461	33,463
Other comprehensive income	(857)	(21,467)
Balance	56,604	11,996
Net of tax
Balance	2,476,485	2,736,941
Other comprehensive income	1,319	32,886
Balance	2,505,994	2,471,734
Accumulated Other Comprehensive Loss
Net of tax
Balance	(88,011)	(51,259)
Other comprehensive income	1,319	32,886
Balance	(86,692)	(18,373)
Investment securities
Pre-tax Amount
Unrealized net gains (losses) arising during the period	1,578	80,910
Reclassification of net gains to net income		(25,728)
Other comprehensive income	1,578	55,182
Income Tax Benefit (Expense)
Unrealized net gains (losses) arising during the period	(621)	(31,958)
Reclassification of net gains to net income		10,164
Other comprehensive income	(621)	(21,794)
Net of tax
Balance	(59,958)	(25,106)
Unrealized net gains (losses) arising during the period	957	48,952
Reclassification of gains to net income		(15,564)
Other comprehensive income	957	33,388
Balance	(59,001)	8,282
Cash flow derivative hedges
Pre-tax Amount
Unrealized net gains (losses) arising during the period	598	(829)
Other comprehensive income	598	(829)
Income Tax Benefit (Expense)
Unrealized net gains (losses) arising during the period	(236)	327
Other comprehensive income	(236)	327
Net of tax
Balance	2,184	730
Unrealized net gains (losses) arising during the period	362	(502)
Other comprehensive income	362	(502)
Balance	$ 2,546	$ 228