Stock Incentive Plans - Stock Option Activity (Details) - Stock Option - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended		12 Months Ended
	Mar. 31, 2019	Mar. 31, 2018	Dec. 31, 2018
Number Of Shares (in thousands)
Outstanding, beginning balance (in shares)	1,518
Options exercised (in shares)	(177)
Options forfeited/expired/canceled (in shares)	(15)
Options granted (in shares)	248
Outstanding, ending balance (in shares)	1,574	1,600	1,518
Exercisable, end of period (in shares)	1,107
Vested and expected to vest, end of period (in shares)	1,553
Weighted Average Exercise Price
Outstanding, beginning balance (in usd per share)	$ 21.18
Options exercised (in usd per share)	18.72
Options forfeited/expired/canceled (in usd per share)	29.37
Options granted (in usd per share)	26.49
Outstanding, ending balance (in usd per share)	22.21		$ 21.18
Exercisable, end of period (in usd per share)	19.81
Vested and expected to vest, end of period (in usd per share)	$ 22.14
Other Disclosures
Outstanding, weighted-average remaining contractual term	4 years 1 month 34 days		3 years 8 months 30 days
Exercisable, weighted-average remaining contractual term	3 years 1 month 11 days
Vested and expected to vest, weighted-average remaining contractual term	4 years 1 month 24 days
Outstanding, aggregated intrinsic value	$ 12,162		$ 7,145
Exercisable, aggregated intrinsic value	11,028
Vested and expected to vest, aggregated intrinsic value	$ 12,109