Condensed Financial Information - Parent Company Only Cash Flows (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Cash Flows From Operating Activities:
Net Income	$ 161,625	$ 149,502	$ 157,894
Adjustments to Reconcile Net Income to Net Cash Provided by Operating Activities [Abstract]
Stock-based compensation	6,556	5,938	5,865
Excess tax benefits from stock-based compensation	(964)	(201)	(81)
(Increase) decrease in other assets	(29,940)	(22,987)	(23,619)
Loss on redemption of trust preferred securities	0	5,626	0
(Decrease) increase in other liabilities and payable to non-bank subsidiaries	4,427	4,928	1,522
Total adjustments	23,785	28,042	52,815
Net cash provided by operating activities	185,410	177,544	210,709
Cash Flows From Investing Activities
Net cash used in investing activities	(1,000,416)	(818,027)	(275,448)
Cash Flows From Financing Activities:
Repayments of long-term debt	(236,640)	(540,079)	(6,621)
Additions to long-term debt	215,884	347,778	262,113
Net proceeds from issuance of common stock	16,167	10,607	8,201
Excess tax benefits from stock-based compensation	964	201	81
Dividends paid	(69,382)	(65,361)	(64,028)
Acquisition of treasury stock	(18,545)	(50,000)	(175,255)
Deferred accelerated stock repurchase payment	0	0	(20,000)
Deferred accelerated stock repurchase payment	18,545	50,000	175,255
Net cash provided by (used in) financing activities	832,649	635,901	(48,099)
Net Increase (Decrease) in Cash and Cash Equivalents	17,643	(4,582)	(112,838)
Parent
Cash Flows From Operating Activities:
Net Income	161,625	149,502	157,894
Adjustments to Reconcile Net Income to Net Cash Provided by Operating Activities [Abstract]
Stock-based compensation	6,556	5,938	5,865
Excess tax benefits from stock-based compensation	(964)	(201)	(81)
(Increase) decrease in other assets	(16,585)	2,806	(7,120)
Equity in undistributed net income of subsidiaries	(65,340)	(58,884)	(39,895)
Loss on redemption of trust preferred securities	0	5,626	0
(Decrease) increase in other liabilities and payable to non-bank subsidiaries	(5,928)	106,490	37,354
Total adjustments	(82,261)	61,775	(3,877)
Net cash provided by operating activities	79,364	211,277	154,017
Cash Flows From Financing Activities:
Repayments of long-term debt	0	(254,640)	0
Additions to long-term debt	0	147,779	97,113
Net proceeds from issuance of common stock	16,167	10,607	8,201
Excess tax benefits from stock-based compensation	964	201	81
Dividends paid	(69,382)	(65,361)	(64,028)
Acquisition of treasury stock	(18,545)	(50,000)	(175,255)
Deferred accelerated stock repurchase payment	0	0	(20,000)
Net cash provided by (used in) financing activities	(70,796)	(211,414)	(153,888)
Net Increase (Decrease) in Cash and Cash Equivalents	8,568	(137)	129
Cash and Cash Equivalents at Beginning of Year	0	137	8
Cash and Cash Equivalents at End of Year	$ 8,568	$ 0	$ 137