Investment Securities - Available-For-Sale Investment (Details) - USD ($) $ in Thousands	Sep. 30, 2018	Jan. 01, 2018	Dec. 31, 2017
Total debt securities available-for-sale
Amortized Cost	$ 2,806,281		$ 1,975,257
Unrealized Gains	1,696		3,605
Unrealized Losses	71,097		17,140
Fair Value	2,736,880		1,961,722
Total equity securities
Amortized Cost			1,389
Unrealized Gains			435
Unrealized Losses			0
Fair Value			1,824
Total
Amortized Cost	2,806,281		1,976,646
Unrealized Gains			4,040
Unrealized Losses			17,140
Total	2,736,880		1,963,546
Government and government-sponsored agencies
Total debt securities available-for-sale
Amortized Cost	258,643		203,099
Unrealized Gains	14		765
Unrealized Losses	4,204		948
Fair Value	254,453		202,916
State and political subdivisions
Total debt securities available-for-sale
Amortized Cost	506,277		350,088
Unrealized Gains	187		310
Unrealized Losses	14,555		4,428
Fair Value	491,909		345,970
Residential mortgage-backed securities
Total debt securities available-for-sale
Amortized Cost	182,983		151,752
Unrealized Gains	6		5
Unrealized Losses	5,968		1,626
Fair Value	177,021		150,131
Collateralized mortgage obligations
Total debt securities available-for-sale
Amortized Cost	1,517,172		1,042,240
Unrealized Gains	0		89
Unrealized Losses	39,354		8,484
Fair Value	1,477,818		1,033,845
Corporate bonds
Total debt securities available-for-sale
Amortized Cost	293,828		193,230
Unrealized Gains	485		1,156
Unrealized Losses	6,908		1,592
Fair Value	287,405		192,794
Trust preferred securities
Total debt securities available-for-sale
Amortized Cost	47,378		34,848
Unrealized Gains	1,004		1,280
Unrealized Losses	108		62
Fair Value	$ 48,274		36,066
Preferred stock
Total equity securities
Amortized Cost			1,389
Unrealized Gains			435
Unrealized Losses			0
Fair Value		$ 1,800	$ 1,824

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Amount, before tax, of unrealized gain in accumulated other comprehensive income (AOCI) on investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale).

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