Consolidated Statements of Comprehensive Income (Unaudited) (USD $) In Thousands, unless otherwise specified	3 Months Ended				6 Months Ended
	Jun. 30, 2014		Jun. 30, 2013		Jun. 30, 2014	Jun. 30, 2013
Statement of Comprehensive Income [Abstract]
Net income	$ 14,746		$ 12,758		$ 28,129	$ 25,010
Unrealized gains (losses) on securities
Change in fair value of securities available for sale	2,383		(4,586)		4,354	(5,371)
Less: net security gains (losses) reclassified into earnings	(12)		3		42	(3)
Net change in fair value of securities available for sale	2,395		(4,589)		4,312	(5,368)
Unrealized gains (losses) on cash flow hedges
Change in fair value of cash flow hedges	(287)		765		(464)	763
Less: net cash flow hedge losses reclassified into earnings	(1,292)		(854)		(1,971)	(1,691)
Net change in fair value of cash flow hedges	1,005		1,619		1,507	2,454
Net gain (loss) during the period and amortization of certain costs included in net periodic retirement costs	(39)	[1]	42	[1]	(78)	43
Total other comprehensive income (loss)	3,361		(2,928)		5,741	(2,871)
Total comprehensive income	$ 18,107		$ 9,830		$ 33,870	$ 22,139

[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.