Consolidated Statements of Comprehensive Income (Unaudited) (USD $) In Thousands, unless otherwise specified	3 Months Ended				9 Months Ended
	Sep. 30, 2014		Sep. 30, 2013		Sep. 30, 2014	Sep. 30, 2013
Statement of Comprehensive Income [Abstract]
Net income	$ 15,738		$ 14,655		$ 43,867	$ 39,665
Unrealized gains (losses) on securities
Change in fair value of securities available for sale	(810)		(148)		3,544	(5,517)
Other Comprehensive Income (Loss), Reclassification Adjustment from AOCI for Sale of Securities, Net of Tax	40		0		82	(3)
Net change in fair value of securities available for sale	(850)		(148)		3,462	(5,514)
Unrealized gains (losses) on cash flow hedges
Change in fair value of cash flow hedges	149		(411)		(315)	350
Less: net cash flow hedge losses reclassified into earnings	(429)		(866)		(2,400)	(2,557)
Net change in fair value of cash flow hedges	578		455		2,085	2,907
Net gain (loss) during the period and amortization of certain costs included in net periodic retirement costs	(39)	[1]	30	[1]	(117)	73
Total other comprehensive income (loss)	(311)		337		5,430	(2,534)
Total comprehensive income	$ 15,427		$ 14,992		$ 49,297	$ 37,131

[1] The amortization of prior service costs is included in the computation of net periodic pension cost as disclosed in the Employee Benefit Plans footnote in the Company's Annual Report on Form 10-K for the year ended December 31, 2013, filed with the Securities and Exchange Commission.