Consolidated Statements Of Changes In Shareholders' Equity - USD ($) $ in Thousands	Total	Preferred stock	Common stock	Surplus	Treasury stock	Retained earnings	Accumulated other comprehensive income (loss)	Series A preferred stock	Series A preferred stock Preferred stock	Series A preferred stock Common stock	Series A preferred stock Surplus	Series A preferred stock Treasury stock	Series A preferred stock Retained earnings	Series A preferred stock Accumulated other comprehensive income (loss)	Series C preferred stock	Series C preferred stock Preferred stock	Series C preferred stock Common stock	Series C preferred stock Surplus	Series C preferred stock Treasury stock	Series C preferred stock Retained earnings	Series C preferred stock Accumulated other comprehensive income (loss)
Balance at Dec. 31, 2012	$ 1,804,705	$ 176,406	$ 37,108	$ 1,036,295	$ (7,838)	$ 555,023	$ 7,711
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	137,210	0	0	0	0	137,210	0
Other comprehensive income (loss), net of tax	(70,747)	0	0	0	0	0	(70,747)
Cash dividends declared on common stock	(6,903)	0	0	0	0	(6,903)	0
Dividends on preferred stock	(8,325)	0	0	0	0	(8,325)	0
Accretion on preferred stock	0	70	0	0	0	(70)	0
Stock-based compensation	6,799	0	0	6,799	0	0	0
Conversion of Series A C preferred stock to common stock								$ 0	$ (49,976)	$ 1,944	$ 48,032	$ 0	$ 0	$ 0	$ 0	$ (23)	$ 1	$ 22	$ 0	$ 0	$ 0
Settlement of prepaid common stock purchase contracts	0	0	5,870	(14,212)	8,342	0	0
Common stock issued for:
Acquisitions	23,070	0	648	22,422	0	0	0
Exercise of stock options and warrants	10,770	0	372	13,613	(3,215)	0	0
Restricted stock awards	38	0	145	182	(289)	0	0
Employee stock purchase plan	2,459	0	62	2,397		0	0
Director compensation plan	1,513	0	31	1,482		0	0
Balance at Dec. 31, 2013	1,900,589	126,477	46,181	1,117,032	(3,000)	676,935	(63,036)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	151,398	0	0	0	0	151,398
Other comprehensive income (loss), net of tax	25,704	0	0	0	0		25,704
Cash dividends declared on common stock	(18,610)	0	0	0	0	(18,610)
Dividends on preferred stock	(6,323)	0	0	0	0	(6,323)
Stock-based compensation	7,754	0	0	7,754	0	0
Conversion of Series A C preferred stock to common stock															0	(10)	1	9	0	0	0
Common stock issued for:
Exercise of stock options and warrants	4,639	0	538	4,414	(313)	0	0
Restricted stock awards	18	0	76	178	(236)	0	0
Employee stock purchase plan	3,004	0	65	2,939	0	0	0
Director compensation plan	1,649	0	20	1,629		0	0
Balance at Dec. 31, 2014	2,069,822	126,467	46,881	1,133,955	(3,549)	803,400	(37,332)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	156,749	0	0	0	0	156,749	0
Other comprehensive income (loss), net of tax	(25,376)	0	0	0	0	0	(25,376)
Cash dividends declared on common stock	(21,069)	0	0	0	0	(21,069)	0
Dividends on preferred stock	(10,869)	0	0	0	0	(10,869)	0
Stock-based compensation	9,656	0	0	9,656	0	0	0
Issuance of Series D preferred stock	120,842	125,000	0	(4,158)	0	0	0
Conversion of Series A C preferred stock to common stock															$ 0	$ (180)	$ 4	$ 176	$ 0	$ 0	$ 0
Common stock issued for:
Acquisitions	38,723	0	811	37,912	0	0	0
Exercise of stock options and warrants	9,606	0	587	9,149	(130)	0	0
Restricted stock awards	(243)	0	108	(57)	(294)	0	0
Employee stock purchase plan	2,750	0	58	2,692	0	0	0
Director compensation plan	1,683	0	20	1,663	0	0	0
Balance at Dec. 31, 2015	$ 2,352,274	$ 251,287	$ 48,469	$ 1,190,988	$ (3,973)	$ 928,211	$ (62,708)