Share-Based Compensation (Details) - USD ($) $ / shares in Units, $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock-based compensation expense recognized	$ 4,394	$ 6,380	$ 3,846
Unrecognized Compensation Cost	2,900
Unrecognized compensation cost not expected to be recognized	$ 0
Expiration date of 2007 Stock Incentive Plan	May 20, 2024
Outstanding:
Beginning Balance (in shares)	77,000	105,000
Beginning Balance, weighted average exercise price (in dollars per share)	$ 16.29
Granted (in shares)	0	0	0
Granted, weighted average exercise price (in dollars per share)	$ 0	$ 0	$ 0
Stock options exercised (in shares)	77,334	27,619	0
Exercised, weighted average exercise price (in dollars per share)	$ 16.29		$ 0
Ending Balance (in shares)	0	77,000	105,000
Ending balance, weighted average exercise price (in dollars per share)		$ 16.29
Vested and expected to vest (in shares)	0	77,000	105,000
Exercisable (in shares)
Share-based Compensation Arrangement by Share-based Payment Award, Options, Exercisable, Number	0	77,000	105,000
Weighted-average remaining contractual life of all exercisable options (in years)	0 years
Stock price per share (in dollars per share)	$ 0
Share-based compensation arrangement by share-based payment award, options, exercisable, intrinsic value	$ 0
Intrinsic value under share based compensation scheme	$ 20	$ 85	$ 0
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]
Options outstanding, number of options (in shares)	0
Options outstanding, weighted average remaining contractual life (in years)	0 years
Options outstanding, weighted average exercise price (in dollars per share)	$ 0
Stock Options [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock-based compensation expense recognized	$ 0	0	0
Unrecognized Compensation Cost	$ 0
Weighted Average Remaining Amortization Periods (in years)	0 years
Restricted Stock Units (RSUs) [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock-based compensation expense recognized	$ 4,231	$ 6,263	$ 3,705
Unrecognized Compensation Cost	$ 2,900
Weighted Average Remaining Amortization Periods (in years)	1 year
Exercisable (in shares)
Expected to vest	986,000	1,004,000	806,000
Outstanding:
Balance (in shares)	1,004,000	1,028,000	1,147,000
Granted (in shares)	304,000	353,000	349,000
Vested (in shares)	(322,000)	(155,000)	(182,000)
Cancelled or forfeited (in shares)	0	(222,000)	(286,000)
Balance (in shares)	986,000	1,004,000	1,028,000
Beginning balance, Weighted average grant-date fair value (in dollars per share)	$ 12.74	$ 13.24	$ 12.75
Granted, Weighted average grant-date fair value (in dollars per share)	15.52	11.35	13.60
Vested, Weighted average grant-date fair value (in dollars per share)	13.54	12.27	11.41
Forfeitures, Weighted average grant date fair value	0	13.19	12.89
Ending balance, Weighted average grant-date fair value (in dollars per share)	$ 13.34	$ 12.74	$ 13.24
Phantom Stock Units [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock-based compensation expense recognized	$ 163	$ 117	$ 141
Unrecognized Compensation Cost	$ 0
Weighted Average Remaining Amortization Periods (in years)	0 years
Outstanding:
Balance (in shares)	145,000	132,000	119,000
Granted (in shares)	10,000	10,000	10,000
Dividend equivalents issued	2,000	3,000	3,000
Redeemed for common stock (in shares)	0	0	0
Balance (in shares)	157,000	145,000	132,000
Granted, Weighted average grant-date fair value (in dollars per share)	$ 16.25	$ 11.71	$ 14.09
Performance Vested Restricted Stock Units [Member] | Scheduled to Vest January 1, 2017 [Member]
Exercisable (in shares)
Share Based Compensation Arrangement By Share Based Payment Award Equity Instruments Other Than Options Not Expected To Vest Outstanding Number	0
Expected to vest	202,000
Outstanding:
Balance (in shares)	202,000
Performance Vested Restricted Stock Units [Member] | Scheduled to Vest January 1, 2018 [Member]
Exercisable (in shares)
Share Based Compensation Arrangement By Share Based Payment Award Equity Instruments Other Than Options Not Expected To Vest Outstanding Number	0
Expected to vest	213,000
Outstanding:
Balance (in shares)	213,000
Performance Vested Restricted Stock Units [Member] | Scheduled to Vest January 1, 2019 [Member]
Exercisable (in shares)
Share Based Compensation Arrangement By Share Based Payment Award Equity Instruments Other Than Options Not Expected To Vest Outstanding Number	0
Expected to vest	167,000
Outstanding:
Balance (in shares)	167,000
2007 Stock Incentive Plan [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Maximum number of shares authorized under restricted stock, unrestricted stock, RSU's and stock options to officers, employees and non-employee directors (in shares)	6,500,000
Exercisable (in shares)
Available for future grants (in shares)	3,158,000