Securities (Details) - Securities Portfolio - USD ($) $ in Thousands	Mar. 31, 2017	Dec. 31, 2016
Schedule of Trading Securities and Other Trading Assets [Line Items]
Trading Securities	$ 19,130	$ 17,920
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	1,971,960	1,957,584
Gross Unrealized Gains	5,310	4,562
Gross Unrealized Losses	(40,146)	(42,696)
Fair Value	1,937,124	1,919,450
Schedule of Held-to-maturity Securities [Line Items]
Amortized Cost	17,742	22,291
Municipal securities, Fair Value	15,118
U.S. treasury securities
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	48,574	48,581
Gross Unrealized Gains	23	26
Gross Unrealized Losses	(81)	(66)
Fair Value	48,516	48,541
U.S. agency securities
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	180,894	183,528
Gross Unrealized Gains	518	519
Gross Unrealized Losses	(382)	(410)
Fair Value	181,030	183,637
Collateralized mortgage obligations (CMOs)
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	1,066,439	1,064,130
Gross Unrealized Gains	1,039	969
Gross Unrealized Losses	(16,114)	(17,653)
Fair Value	1,051,364	1,047,446
Other mortgage-backed securities (MBSs)
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	357,473	337,139
Gross Unrealized Gains	1,230	1,395
Gross Unrealized Losses	(5,737)	(5,879)
Fair Value	352,966	332,655
Municipal securities
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	263,606	273,319
Gross Unrealized Gains	2,092	1,245
Gross Unrealized Losses	(2,988)	(3,718)
Fair Value	262,710	270,846
Trust-preferred collateralized debt obligations (CDOs)
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	47,728	47,681
Gross Unrealized Gains	260	261
Gross Unrealized Losses	(14,552)	(14,682)
Fair Value	33,436	33,260
Equity securities
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	7,246	3,206
Gross Unrealized Gains	148	147
Gross Unrealized Losses	(292)	(288)
Fair Value	7,102	3,065
Trading Securities
Schedule of Trading Securities and Other Trading Assets [Line Items]
Trading Securities	19,130	17,920
Municipal securities
Schedule of Held-to-maturity Securities [Line Items]
Amortized Cost	17,742	22,291
Municipal securities, Gross Unrealized Gains	0	0
Municipal securities, Gross Unrealized Losses	(2,624)	(4,079)
Municipal securities, Fair Value	$ 15,118	$ 18,212

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

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