Condensed Financial Information - Parent Company Only Cash Flows (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Cash Flows From Operating Activities:
Net Income	$ 149,502	$ 157,894	$ 161,840
Adjustments to Reconcile Net Income to Net Cash Provided by Operating Activities [Abstract]
Stock-based compensation	5,938	5,865	5,330
Excess tax benefits from stock-based compensation	(201)	(81)	(302)
Decrease (increase) in other assets	(9,931)	(8,803)	37,236
Loss on redemption of trust preferred securities	5,626	0	0
Increase in other liabilities and payable to non-bank subsidiaries	(8,128)	(13,294)	(29,344)
Total adjustments	27,460	52,478	139,777
Net cash provided by operating activities	176,962	210,372	301,617
Cash Flows From Investing Activities
Net cash used in investing activities	(818,027)	(275,448)	(598,747)
Cash Flows From Financing Activities:
Repayments of long-term debt	(539,497)	(6,284)	(10,669)
Additions to long-term debt	347,778	262,113	0
Net proceeds from issuance of common stock	10,607	8,201	9,936
Excess tax benefits from stock-based compensation	201	81	302
Dividends paid	(65,361)	(64,028)	(46,525)
Acquisition of treasury stock	(50,000)	(175,255)	(90,927)
Deferred accelerated stock repurchase payment	0	(20,000)	0
Deferred accelerated stock repurchase payment	50,000	175,255	90,927
Net cash provided by (used in) financing activities	636,483	(47,762)	259,370
Net (Decrease) Increase in Cash and Cash Equivalents	(4,582)	(112,838)	(37,760)
Parent
Cash Flows From Operating Activities:
Net Income	149,502	157,894	161,840
Adjustments to Reconcile Net Income to Net Cash Provided by Operating Activities [Abstract]
Stock-based compensation	5,938	5,865	5,330
Excess tax benefits from stock-based compensation	(201)	(81)	(302)
Decrease (increase) in other assets	2,806	(7,120)	1,893
Equity in undistributed net income of subsidiaries	(58,884)	(39,895)	(68,525)
Loss on redemption of trust preferred securities	5,626	0	0
Increase in other liabilities and payable to non-bank subsidiaries	106,490	37,354	26,946
Total adjustments	61,775	(3,877)	(34,658)
Net cash provided by operating activities	211,277	154,017	127,182
Cash Flows From Financing Activities:
Repayments of long-term debt	(254,640)	0	0
Additions to long-term debt	147,779	97,113	0
Net proceeds from issuance of common stock	10,607	8,201	9,936
Excess tax benefits from stock-based compensation	201	81	302
Dividends paid	(65,361)	(64,028)	(46,525)
Acquisition of treasury stock	(50,000)	(175,255)	(90,927)
Deferred accelerated stock repurchase payment	0	(20,000)	0
Net cash provided by (used in) financing activities	(211,414)	(153,888)	(127,214)
Net (Decrease) Increase in Cash and Cash Equivalents	(137)	129	(32)
Cash and Cash Equivalents at Beginning of Year	137	8	40
Cash and Cash Equivalents at End of Year	$ 0	$ 137	$ 8