Investment Securities (Summary of Amortized Cost and Fair Value of Available-for-Sale Investment Securities) (Details) - USD ($) $ in Thousands	Dec. 31, 2018	Jan. 01, 2018	Dec. 31, 2017
Debt securities
Total	$ 3,069,645		$ 1,975,257
Unrealized Gains	5,601		3,605
Unrealized Losses	53,414		17,140
Fair Value	3,021,832		1,961,722
Equity securities
Total			1,389
Unrealized Gains			435
Unrealized Losses			0
Fair Value			1,824
Amortized Cost			1,976,646
Unrealized Gains			4,040
Unrealized Losses			17,140
Fair Value			1,963,546
Government and government-sponsored enterprises
Debt securities
Total	354,342		203,099
Unrealized Gains	713		765
Unrealized Losses	3,355		948
Fair Value	351,700		202,916
State and political subdivisions
Debt securities
Total	523,178		350,088
Unrealized Gains	1,141		310
Unrealized Losses	8,033		4,428
Fair Value	516,286		345,970
Residential mortgage-backed securities
Debt securities
Total	216,990		151,752
Unrealized Gains	261		5
Unrealized Losses	3,823		1,626
Fair Value	213,428		150,131
Collateralized mortgage obligations
Debt securities
Total	1,623,415		1,042,240
Unrealized Gains	2,903		89
Unrealized Losses	25,020		8,484
Fair Value	1,601,298		1,033,845
Corporate bonds
Debt securities
Total	304,243		193,230
Unrealized Gains	259		1,156
Unrealized Losses	11,439		1,592
Fair Value	293,063		192,794
Trust preferred securities
Debt securities
Total	47,477		34,848
Unrealized Gains	324		1,280
Unrealized Losses	1,744		62
Fair Value	$ 46,057		36,066
Preferred stock
Equity securities
Total			1,389
Unrealized Gains			435
Unrealized Losses			0
Fair Value		$ 1,800	$ 1,824

Equity Securities, Available-for-sale, Fair Value to Amortized Cost [Abstract]

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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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