Income Taxes (Narrative) (Details) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Operating Loss Carryforwards [Line Items]
Income before taxes	$ 88,332	$ 85,054	$ 79,971	$ 78,497	$ 56,408	$ 62,197	$ 70,126	$ 63,035	$ 331,854	$ 251,765	$ 246,431
Tax benefit (expense) from stock-based compensation arrangements									230	(1,900)	(594,000)
AMT credt carryforward	1,872				$ 1,498				1,872	1,498
Unrecognized tax benefits	7,600								7,600
Interest income accrued on unrecognized tax benefits	521								521
Domestic Tax Authority
Operating Loss Carryforwards [Line Items]
Net operating loss carryforwards	21,800								21,800
Foreign Tax Authority
Operating Loss Carryforwards [Line Items]
Net operating loss carryforwards	$ 13,300								13,300
Geographic distribution, foreign
Operating Loss Carryforwards [Line Items]
Income before taxes									$ 7,000	$ 3,900	$ 3,800
Minimum | Domestic Tax Authority
Operating Loss Carryforwards [Line Items]
Net operating loss expiration date									Jan. 01, 2028
Maximum | Domestic Tax Authority
Operating Loss Carryforwards [Line Items]
Net operating loss expiration date									Dec. 31, 2035
Maximum | Foreign Tax Authority
Operating Loss Carryforwards [Line Items]
Net operating loss expiration date									Dec. 31, 2035