Income Taxes - Impact of Adoption of New Accounting Pronouncement (Details) (USD $)	3 Months Ended		9 Months Ended					3 Months Ended			12 Months Ended	3 Months Ended	9 Months Ended			9 Months Ended
	Sep. 30, 2014	Sep. 30, 2013	Sep. 30, 2014	Sep. 30, 2013	Dec. 31, 2013	Dec. 31, 2012		Sep. 30, 2014 Accounting Standards Update 2014-01 [Member]	Dec. 31, 2013 Accounting Standards Update 2014-01 [Member]	Dec. 31, 2012 Accounting Standards Update 2014-01 [Member]	Dec. 31, 2013 Accounting Standards Update 2014-01 [Member] Premises and Equipment [Member]	Sep. 30, 2014 Accounting Standards Update 2014-01 [Member] As previously reported [Member]	Sep. 30, 2013 Accounting Standards Update 2014-01 [Member] As previously reported [Member]	Dec. 31, 2013 Accounting Standards Update 2014-01 [Member] As previously reported [Member]		Sep. 30, 2013 Accounting Standards Update 2014-01 [Member] Scenario, Adjustment [Member]	Dec. 31, 2013 Accounting Standards Update 2014-01 [Member] Scenario, Adjustment [Member]
Consolidated Balance Sheet:
Deferred tax assets, net	$ 67,501,000		$ 67,501,000		$ 80,688,000									$ 79,374,000			$ 80,688,000
Other assets	205,383,000		205,383,000		185,221,000									186,288,000	[1]		185,221,000
Stockholders' equity	1,003,122,000	826,472,000	1,003,122,000	826,472,000	855,498,000	759,421,000	[2]							855,251,000			855,498,000
Consolidated Income Statement:
Non-interest income	6,226,000	4,129,000	16,834,000	20,690,000				4,129,000				2,625,000	17,386,000			20,690,000
Income tax expense (benefit)	12,949,000	10,390,000	34,279,000	25,838,000				10,390,000				9,288,000	22,913,000			25,838,000
Income from continuing operations	40,919,000	28,623,000	108,700,000	83,711,000				28,623,000				28,221,000	83,332,000			83,711,000
Net income	40,919,000	28,594,000	107,542,000	83,551,000				28,594,000				28,192,000	83,172,000			83,551,000
Net income available to common shareholders	40,566,000	28,242,000	106,484,000	82,493,000				28,242,000				27,840,000	82,114,000			82,493,000
Basic (usd per share)	$ 0.47	$ 0.33	$ 1.24	$ 0.97				$ 0.33				$ 0.32	$ 0.96			$ 0.96
Diluted (usd per share)	$ 0.46	$ 0.33	$ 1.23	$ 0.96				$ 0.33				$ 0.32	$ 0.95			$ 0.95
Reclassification adjustment											(14,600,000)
Cumulative effect to stockholders' equity									200,000	(200,000)
Investment in Low Income Housing Tax Credit	123,000,000		123,000,000
Deferred Tax Assets, Tax Credit Carryforwards	55,500,000		55,500,000
Amortization of Low Income Housing Tax Credits	$ 3,000,000		$ 9,300,000

[1] Includes a $14.6 million reclassification from premises and equipment, net.

[2] As adjusted, see "Note 10. Income Taxes" to the Unaudited Consolidated Financial Statements.