Securities - Securities Portfolio (Details) - USD ($) $ in Thousands	Sep. 30, 2017	Dec. 31, 2016
Schedule of Trading Securities and Other Trading Assets [Line Items]
Trading Securities	$ 20,425	$ 17,920
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	1,763,521	1,957,584
Gross Unrealized Gains	2,837	4,562
Gross Unrealized Losses	(33,374)	(42,696)
Fair Value	1,732,984	1,919,450
Schedule of Held-to-maturity Securities [Line Items]
Amortized Cost	14,638	22,291
Fair Value	12,921
U.S. treasury securities
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	42,567	48,581
Gross Unrealized Gains	14	26
Gross Unrealized Losses	(77)	(66)
Fair Value	42,504	48,541
U.S. agency securities
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	154,666	183,528
Gross Unrealized Gains	303	519
Gross Unrealized Losses	(362)	(410)
Fair Value	154,607	183,637
Collateralized mortgage obligations (CMOs)
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	949,762	1,064,130
Gross Unrealized Gains	459	969
Gross Unrealized Losses	(12,999)	(17,653)
Fair Value	937,222	1,047,446
Other mortgage-backed securities (MBSs)
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	358,746	337,139
Gross Unrealized Gains	307	1,395
Gross Unrealized Losses	(3,580)	(5,879)
Fair Value	355,473	332,655
Municipal securities
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	204,571	273,319
Gross Unrealized Gains	1,294	1,245
Gross Unrealized Losses	(841)	(3,718)
Fair Value	205,024	270,846
Trust-preferred collateralized debt obligations (CDOs)
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	45,851	47,681
Gross Unrealized Gains	275	261
Gross Unrealized Losses	(15,300)	(14,682)
Fair Value	30,826	33,260
Equity securities
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	7,358	3,206
Gross Unrealized Gains	185	147
Gross Unrealized Losses	(215)	(288)
Fair Value	7,328	3,065
Trading Securities
Schedule of Trading Securities and Other Trading Assets [Line Items]
Trading Securities	20,425	17,920
Municipal securities
Schedule of Held-to-maturity Securities [Line Items]
Amortized Cost	14,638	22,291
Gross Unrealized Gains	0	0
Gross Unrealized Losses	(1,717)	(4,079)
Fair Value	$ 12,921	$ 18,212

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

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