CONSOLIDATED STATEMENTS OF COMPREHENSIVE INCOME (Unaudited) - USD ($)	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Statement of Comprehensive Income [Abstract]
Net income	$ 93,747,000	$ 64,442,000	$ 264,122,000	$ 147,181,000
Other comprehensive income (loss), net of tax:
Change in fair value on available-for-sale securities, net of tax	(16,899,000)	(967,000)	(53,167,000)	133,000
Change in fair value of cash flow hedges, net of tax	783,000	239,000	3,453,000	1,307,000
Other Comprehensive Income(Loss), Transfers from Available-for-sale to Held-to-maturity securities, net of tax	(10,000)	(47,000)	(103,000)	(160,000)
Interest Rate Cash Flow Hedge Gain (Loss) Reclassified to Earnings, Net	(145,000)	(139,000)	(429,000)	(204,000)
Net gain on sale of investment securities reclassified from other comprehensive income into net income, net of tax	(8,000)	0	(30,000)	0
Total other comprehensive income (loss), net of tax	(16,279,000)	(914,000)	(50,276,000)	1,076,000
Total comprehensive income	$ 77,468,000	$ 63,528,000	$ 213,846,000	$ 148,257,000