Qualifying Debt Supplemental Schedule - Adoption of ASU 2016-01 (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2014	Sep. 30, 2014	Jun. 30, 2014	Mar. 31, 2014	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
New Accounting Pronouncement, Early Adoption [Line Items]
Retained earnings	$ 22,260				$ 16,639				$ 22,260	$ 16,639	$ (21,546)	$ 8,226
Accumulated other comprehensive income	262,638				85,453				262,638	85,453
Non-interest income	9,479	$ 8,502	$ 5,545	$ 6,242	8,417	$ 6,073	$ 5,599	$ 4,562	29,768	24,651	22,197
Income Tax Expense (Benefit)	19,348	17,133	13,579	14,234	14,111	12,949	10,706	10,624	64,294	48,390	29,830
Net income (loss)	58,526	55,860	39,475	40,383	40,409	40,919	35,538	31,085	194,244	147,951	114,965
Net income available to common shareholders	$ 58,375	$ 55,684	$ 39,228	$ 40,207	$ 40,080	$ 40,566	$ 35,186	$ 30,732	$ 193,494	$ 146,564	$ 113,555
Earnings Per Share, Basic	$ 0.58	$ 0.55	$ 0.44	$ 0.46	$ 0.46	$ 0.47	$ 0.41	$ 0.35	$ 2.05	$ 1.69	$ 1.33
Earnings Per Share, Diluted	$ 0.57	$ 0.55	$ 0.44	$ 0.45	$ 0.46	$ 0.46	$ 0.40	$ 0.35	$ 2.03	$ 1.67	$ 1.31
Accounting Standards Update 2016-01 [Member] | Scenario, Previously Reported [Member]
New Accounting Pronouncement, Early Adoption [Line Items]
Retained earnings		$ 20,643	$ 15,348	$ 23,423
Accumulated other comprehensive income		218,897	159,939	125,467
Non-interest income		13,826	(2,191)	5,933
Income Tax Expense (Benefit)		19,183	10,599	14,118
Net income (loss)		59,134	34,719	40,190
Net income available to common shareholders		$ 58,958	$ 34,472	$ 40,014
Earnings Per Share, Basic		$ 590	$ 390	$ 460
Earnings Per Share, Diluted		$ 580	$ 390	$ 450
Accounting Standards Update 2016-01 [Member] | Scenario, Adjustment [Member]
New Accounting Pronouncement, Early Adoption [Line Items]
Retained earnings		$ 35,276	$ 26,707	$ 39,538
Accumulated other comprehensive income		204,264	148,580	109,352
Non-interest income		8,502	5,545	6,242
Income Tax Expense (Benefit)		17,133	13,579	14,234
Net income (loss)		55,860	39,475	40,383
Net income available to common shareholders		$ 55,684	$ 39,228	$ 40,207
Earnings Per Share, Basic		$ 0.55	$ 0.44	$ 0.46
Earnings Per Share, Diluted		$ 0.55	$ 0.44	$ 0.45