Securities (Details) - Securities Portfolio - USD ($) $ in Thousands	Jun. 30, 2017	Dec. 31, 2016
Schedule of Trading Securities and Other Trading Assets [Line Items]
Trading Securities	$ 19,545	$ 17,920
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	1,936,016	1,957,584
Gross Unrealized Gains	5,844	4,562
Gross Unrealized Losses	(33,612)	(42,696)
Fair Value	1,908,248	1,919,450
Schedule of Held-to-maturity Securities [Line Items]
Amortized Cost	17,353	22,291
Fair Value	14,899
U.S. treasury securities
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	48,568	48,581
Gross Unrealized Gains	19	26
Gross Unrealized Losses	(104)	(66)
Fair Value	48,483	48,541
U.S. agency securities
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	174,757	183,528
Gross Unrealized Gains	599	519
Gross Unrealized Losses	(298)	(410)
Fair Value	175,058	183,637
Collateralized mortgage obligations (CMOs)
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	1,017,896	1,064,130
Gross Unrealized Gains	1,086	969
Gross Unrealized Losses	(12,818)	(17,653)
Fair Value	1,006,164	1,047,446
Other mortgage-backed securities (MBSs)
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	377,043	337,139
Gross Unrealized Gains	1,261	1,395
Gross Unrealized Losses	(4,644)	(5,879)
Fair Value	373,660	332,655
Municipal securities
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	262,906	273,319
Gross Unrealized Gains	2,446	1,245
Gross Unrealized Losses	(950)	(3,718)
Fair Value	264,402	270,846
Trust-preferred collateralized debt obligations (CDOs)
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	47,740	47,681
Gross Unrealized Gains	279	261
Gross Unrealized Losses	(14,565)	(14,682)
Fair Value	33,454	33,260
Equity securities
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	7,106	3,206
Gross Unrealized Gains	154	147
Gross Unrealized Losses	(233)	(288)
Fair Value	7,027	3,065
Trading Securities
Schedule of Trading Securities and Other Trading Assets [Line Items]
Trading Securities	19,545	17,920
Municipal securities
Schedule of Held-to-maturity Securities [Line Items]
Amortized Cost	17,353	22,291
Gross Unrealized Gains	0	0
Gross Unrealized Losses	(2,454)	(4,079)
Fair Value	$ 14,899	$ 18,212

Amount of investment in debt and equity securities categorized neither as held-to-maturity nor trading.

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