Stock-Based Compensation Plans (Details) $ / shares in Units, $ in Thousands	12 Months Ended
	Dec. 31, 2018 USD ($) director $ / shares shares	Dec. 31, 2017 USD ($) $ / shares shares	Dec. 31, 2016 USD ($) shares
Unrecognized compensation cost and vesting period
Unrecognized compensation costs related to unvested stock-based compensation arrangements | $	$ 10,300
Weighted-average period for recognition of unrecognized stock-based compensation expense	2 years 1 month 6 days
Other disclosures
Stock-based compensation expense recognized in operating expenses | $	$ 10,356	$ 12,744	$ 13,113
Requisite service period for options to vest	4 years
Tax benefit of stock-based compensation expense in provision for income taxes | $	$ 2,476	4,575	4,757
Allocated Share-based Compensation Expense, Net of Tax | $	7,880	8,169	8,356
Share-based Compensation Arrangement by Share-based Payment Award, Options, Vested in Period, Fair Value | $	15,372	11,043	13,186
Issuance of Company’s common stock | $	695	6,610	7,976
Employee Service Share-based Compensation, Tax Benefit from Exercise of Stock Options | $	$ 0	$ 0	$ 251
Stock Bonus Plan
Other disclosures
Shares issued and committed to issue | shares	9,000	12,000	10,000
Stock-based compensation expense recognized in operating expenses | $	$ 800	$ 1,200	$ 800
Restricted Stock Units
Restricted stock unit activity
Outstanding at the beginning of the period (in shares) | shares	696,000
Awarded (in shares) | shares	189,167
Vested (in shares) | shares	(263,000)
Forfeited (in shares) | shares	(18,000)
Outstanding at the end of the period (in shares) | shares	604,000	696,000
Outstanding and expected to vest at the end of the period (in shares) | shares	598,000
Weighted-Average Exercise Price
Outstanding at the beginning of the period (in dollars per share)	$ 35.34
Awarded (in dollars per share)	54.99
Vested (in dollars per share)	35.23
Forfeited (in dollars per share)	39.23
Outstanding at the end of the period (in dollars per share)	41.37	$ 35.34
Outstanding and expected to vest at the end of the period (in dollars per share)	$ 41.32
Aggregate Intrinsic Value
Outstanding at the end of the period (in dollars) | $	$ 32,669	$ 39,609
Outstanding and expected to vest at end of the period (in dollars) | $	$ 32,388
Closing price per share (in dollars per share)	$ 54.13
Total intrinsic value of awards vested (in dollars) | $	$ 9,800	$ 10,800	10,300
Weighted-Average Exercise Price
Outstanding at the beginning of the period (in dollars per share)	$ 35.34
Forfeited (in dollars per share)	39.23
Outstanding at the end of the period (in dollars per share)	$ 41.37	$ 35.34
Aggregate Intrinsic Value
Outstanding at the end of the period (in dollars) | $	$ 32,669	$ 39,609
Non-Qualified Stock Options
Weighted-Average Exercise Price
Outstanding at the beginning of the period (in dollars per share)	$ 29.66
Forfeited (in dollars per share)	29.66
Outstanding at the end of the period (in dollars per share)	$ 0	$ 29.66
Aggregate Intrinsic Value
Outstanding at the end of the period (in dollars) | $	$ 0	$ 780
Non-Qualified Stock Options activity
Outstanding at the beginning of the period (in shares) | shares	28,000
Exercised (in shares) | shares	(23,000)
Forfeited (in shares) | shares	(5,000)
Outstanding at the end of the period (in shares) | shares	0	28,000
Weighted-Average Exercise Price
Outstanding at the beginning of the period (in dollars per share)	$ 29.66
Exercised (in dollars per share)	29.66
Forfeited (in dollars per share)	29.66
Outstanding at the end of the period (in dollars per share)	$ 0	$ 29.66
Weighted-Average Remaining Contractual Life
Outstanding at the end of the period		3 days
Aggregate Intrinsic Value
Outstanding at the end of the period (in dollars) | $	$ 0	$ 780
Total intrinsic value of stock options exercised (in dollars) | $	$ 700	$ 4,600	$ 3,100
Non-Qualified Stock Options | 2011 Plan
Stock-Based Compensation
Maximum common stock shares that may be issued under plan | shares	16,300,000
Independent directors | Restricted Stock Units
Aggregate Intrinsic Value
Number Of Directors | director	8
Foreign employees
Other disclosures
Shares issued and committed to issue | shares	5,500
Shares expected to be settled In cash | shares	3,500