Stock Compensation and Share Repurchase Plan (Narrative) (Details) - USD ($)	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Shareholders Equity and Share-Based Payments [Line Items]
Compensation cost	$ 9,612,000	$ 9,790,000	$ 14,383,000
Proceeds from stock options exercised	961,000	2,626,000	1,481,000
Income tax benefits received	2,700,000	5,900,000	5,200,000
Net tax benefit from stock options exercised	$ 0	$ 0	$ 552,000
Stock repurchased during period, shares	325,000	635,000	571,000
Stock Options
Shareholders Equity and Share-Based Payments [Line Items]
Compensation cost	$ 8,500,000	$ 8,700,000	$ 13,600,000
Total income tax benefit recognized related to stock-based compensation	3,300,000	3,300,000	5,200,000
Total intrinsic value of options outstanding	863,000
Total intrinsic value of options exercisable	$ 863,000
Share-based compensation arrangement by share-based payment award, options, exercisable, weighted average remaining contractual term	2 years 6 months 15 days
Total intrinsic value of options exercised	$ 382,000	1,200,000	535,000
Proceeds from stock options exercised	354,000	432,000	195,000
Stock option compensation cost	$ 961,000	$ 2,600,000	$ 925,000
Stock repurchase program number of shares tendered	35,000	154,000	52,000
Nonvested Stock
Shareholders Equity and Share-Based Payments [Line Items]
Total unrecognized compensation cost related to nonvested stock awards	$ 0
Restricted Stock
Shareholders Equity and Share-Based Payments [Line Items]
Total unrecognized compensation cost related to nonvested stock awards	$ 8,400,000
Expected recognized over a weighted-average period, years	1 year 2 months 16 days
Share-based compensation award, vesting period	3 years
Fair value of restricted shares	$ 5,800,000	$ 12,000,000	$ 8,600,000
Cancellation of restricted stock shares to pay withholding (in shares)	91,000	279,000	135,000
Restricted Stock Units (RSUs)
Shareholders Equity and Share-Based Payments [Line Items]
Total unrecognized compensation cost related to nonvested stock awards	$ 249,000
Expected recognized over a weighted-average period, years	3 months
Total fair value of restricted stock shares/units vested and released	$ 906,000	$ 2,200,000	$ 4,400,000
Cancellation of restricted stock units to pay withholding (in shares)	17,000	49,000	86,000
Stock Repurchase Plan
Shareholders Equity and Share-Based Payments [Line Items]
Stock repurchase program number of shares authorized, amended	15,000,000
Stock repurchase program, remaining number of shares authorized to be repurchased	10,500,000