Fair Value Measurements and Derivative Instruments (Available-For-Sale Securities) (Details) - USD ($) $ in Thousands	Dec. 31, 2015	Dec. 31, 2014
Schedule of Available-for-sale Securities [Line Items]
Amortized cost	$ 355,226	$ 357,339
Gross unrealized gains	4,528	6,836
Gross unrealized losses	(3,835)	(2,133)
Estimated fair value	355,919	362,042
Investment securities at a loss position for more than 12 months, aggregate unrealized holding losses	2,000	1,000
Investment securities at a loss position for more than 12 months, estimated fair value	36,000	42,000
Investment securities at a loss position for less than 12 months, unrealized holding losses	2,000	1,000
Investment securities at a loss position for less than 12 months, estimated fair value	146,000	88,000
U.S. and foreign governments, agencies and municipalities
Schedule of Available-for-sale Securities [Line Items]
Amortized cost	114,265	135,839
Gross unrealized gains	1,804	2,905
Gross unrealized losses	(1,268)	(764)
Estimated fair value	114,801	137,980
Corporate
Schedule of Available-for-sale Securities [Line Items]
Amortized cost	63,140	66,170
Gross unrealized gains	823	1,569
Gross unrealized losses	(1,079)	(291)
Estimated fair value	62,884	67,448
Mortgage-backed / asset-backed securities
Schedule of Available-for-sale Securities [Line Items]
Amortized cost	177,821	155,330
Gross unrealized gains	1,901	2,362
Gross unrealized losses	(1,488)	(1,078)
Estimated fair value	$ 178,234	$ 156,614