Financial Instruments (Available-for-sale Securities) (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2015	Jun. 30, 2014	Jun. 30, 2015	Jun. 30, 2014	Dec. 31, 2014
Schedule of Available-for-sale Securities [Line Items]
Cost	$ 3,802		$ 3,802		$ 15,050
Gross Unrealized Gains	1,272		1,272		364
Gross Unrealized Losses	0		0		0
Fair Value	5,074		5,074		15,414
Net unrealized gains on available-for-sale securities	816		816		233
Income tax on gains from available-for-sale securities	456		456		131
Proceeds from sales and maturities of securities	15,037	$ 311,926	15,037	$ 342,045
Gross realized gains	3,795	1,298	3,795	1,311
Gross realized losses	0	$ (61)	0	$ (99)
Equity Securities
Schedule of Available-for-sale Securities [Line Items]
Cost	3,802		3,802		15,050
Gross Unrealized Gains	1,272		1,272		364
Gross Unrealized Losses	0		0		0
Fair Value	$ 5,074		$ 5,074		$ 15,414