Capital Stock - Textual (Details) - USD ($)	1 Months Ended		12 Months Ended
	Jan. 31, 2019	Feb. 29, 2016	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016	Nov. 30, 2018	Dec. 31, 2013	Sep. 30, 2010
Equity, Class of Treasury Stock [Line Items]
Treasury stock, common (in shares)			15,530,952	15,366,504	15,162,050
Preferred stock, shares authorized (in shares)			1,000,000
Preferred stock, par or stated value per share (in dollars per share)			$ 0.01
Preferred stock, shares outstanding (in shares)			0	0	0
Treasury stock, shares, acquired (in shares)			362,190	415,418	234,901
Treasury stock issued during period (in shares)			197,742	210,964	375,196
Stock repurchase program, payment for repurchase of convertible notes			$ 0	$ 0	$ 87,271,000
Subsequent event [Member]
Equity, Class of Treasury Stock [Line Items]
Treasury stock, shares, acquired (in shares)	655,666
Treasury shares purchased	$ 5,000,000
Convertible Notes due 2017 [Member] | Senior notes [Member]
Equity, Class of Treasury Stock [Line Items]
Debt instrument, face amount								$ 172,500,000.0
Convertible Notes due 2021 [Member] | Senior notes [Member]
Equity, Class of Treasury Stock [Line Items]
Debt instrument, face amount			$ 100,000,000		$ 100,000,000.0
Share repurchase program [Member]
Equity, Class of Treasury Stock [Line Items]
Treasury stock, shares, acquired (in shares)			0	0	0
Stock repurchase program, authorized amount						$ 100,000,000	$ 33,484,953
Stock repurchase program, remaining authorized repurchase amount			$ 100,000,000
Share repurchase program [Member] | Convertible Notes due 2017 [Member] | Senior notes [Member]
Equity, Class of Treasury Stock [Line Items]
Stock repurchase program, authorized amount					$ 78,100,000.0
Stock repurchase program, repurchased face amount		$ 11,200,000
Stock repurchase program, payment for repurchase of convertible notes		$ 9,200,000
Restricted stock [Member]
Equity, Class of Treasury Stock [Line Items]
Treasury shares purchased			$ 3,900,000	$ 3,200,000	$ 1,200,000