Stock-Based Compensation, Stock Option Activity (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	9 Months Ended	12 Months Ended
Sep. 30, 2019	Dec. 31, 2018
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding [Roll Forward]
Stock Options Shares Outstanding, Beginning balance (in shares)	5,281
Granted	1,050
Exercised	(498)
Forfeited or expired	(114)
September 30, 2019	5,718	5,281
September 30, 2019	3,535
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding, Weighted Average Exercise Price [Abstract]
December 31, 2018	$ 19.09
Granted	22.77
Exercised	15.57
Forfeited	22.42
September 30, 2019	20.01	$ 19.09
Options Exercisable, Weighted Average Exercise Price (in usd per share)	$ 18.12
Stock Options Outstanding, Weighted Average Remaining Contractual Term	6 years 5 months 4 days	6 years 2 months 4 days
Options exercisable, Weighted Average Remaining Contractual Term	5 years 1 month 20 days
Stock Options Outstanding, Aggregate Intrinsic Value	$ 11,541	$ 12,392
Options exercisable, Aggregate Intrinsic Value	$ 10,901

The number of shares into which fully or partially vested stock options outstanding as of the balance sheet date can be currently converted under the option plan.

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Namespace Prefix:	us-gaap_
Data Type:	xbrli:sharesItemType
Balance Type:	na
Period Type:	instant

- Definition

The weighted-average price as of the balance sheet date at which grantees can acquire the shares reserved for issuance on vested portions of options outstanding and currently exercisable under the stock option plan.